diff --git a/README.md b/README.md
index 52eb022..3647345 100644
--- a/README.md
+++ b/README.md
@@ -5,4 +5,7 @@ For more info read [API reference](http://public.innomdc.com/inno-helper/)
 ## Changelog
 
 ### [0.0.4] - 2016-05-20
-- Fixing versions of dependencies
\ No newline at end of file
+- Fixing versions of dependencies
+
+### [0.0.5] - 2017-02-07
+- Preparing for remove the modifiedAt properties.
\ No newline at end of file
diff --git a/composer.json b/composer.json
index 174aaa7..24061b9 100644
--- a/composer.json
+++ b/composer.json
@@ -3,7 +3,7 @@
     "type": "library",
     "description": "Innometrics helper",
     "homepage": "http://www.innometrics.com",
-    "version": "0.0.4",
+    "version": "0.0.5",
     "require": {
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diff --git a/composer.lock b/composer.lock
new file mode 100644
index 0000000..f0d7622
--- /dev/null
+++ b/composer.lock
@@ -0,0 +1,901 @@
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+            "source": {
+                "type": "git",
+                "url": "https://github.com/symfony/polyfill-mbstring.git",
+                "reference": "e79d363049d1c2128f133a2667e4f4190904f7f4"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/symfony/polyfill-mbstring/zipball/e79d363049d1c2128f133a2667e4f4190904f7f4",
+                "reference": "e79d363049d1c2128f133a2667e4f4190904f7f4",
+                "shasum": ""
+            },
+            "require": {
+                "php": ">=5.3.3"
+            },
+            "suggest": {
+                "ext-mbstring": "For best performance"
+            },
+            "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-master": "1.3-dev"
+                }
+            },
+            "autoload": {
+                "psr-4": {
+                    "Symfony\\Polyfill\\Mbstring\\": ""
+                },
+                "files": [
+                    "bootstrap.php"
+                ]
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "Nicolas Grekas",
+                    "email": "p@tchwork.com"
+                },
+                {
+                    "name": "Symfony Community",
+                    "homepage": "https://symfony.com/contributors"
+                }
+            ],
+            "description": "Symfony polyfill for the Mbstring extension",
+            "homepage": "https://symfony.com",
+            "keywords": [
+                "compatibility",
+                "mbstring",
+                "polyfill",
+                "portable",
+                "shim"
+            ],
+            "time": "2016-11-14T01:06:16+00:00"
+        },
+        {
+            "name": "symfony/translation",
+            "version": "v3.2.3",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/symfony/translation.git",
+                "reference": "ca032cc56976d88b85e7386b17020bc6dc95dbc5"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/symfony/translation/zipball/ca032cc56976d88b85e7386b17020bc6dc95dbc5",
+                "reference": "ca032cc56976d88b85e7386b17020bc6dc95dbc5",
+                "shasum": ""
+            },
+            "require": {
+                "php": ">=5.5.9",
+                "symfony/polyfill-mbstring": "~1.0"
+            },
+            "conflict": {
+                "symfony/config": "<2.8"
+            },
+            "require-dev": {
+                "psr/log": "~1.0",
+                "symfony/config": "~2.8|~3.0",
+                "symfony/intl": "~2.8|~3.0",
+                "symfony/yaml": "~2.8|~3.0"
+            },
+            "suggest": {
+                "psr/log": "To use logging capability in translator",
+                "symfony/config": "",
+                "symfony/yaml": ""
+            },
+            "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-master": "3.2-dev"
+                }
+            },
+            "autoload": {
+                "psr-4": {
+                    "Symfony\\Component\\Translation\\": ""
+                },
+                "exclude-from-classmap": [
+                    "/Tests/"
+                ]
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "Fabien Potencier",
+                    "email": "fabien@symfony.com"
+                },
+                {
+                    "name": "Symfony Community",
+                    "homepage": "https://symfony.com/contributors"
+                }
+            ],
+            "description": "Symfony Translation Component",
+            "homepage": "https://symfony.com",
+            "time": "2017-01-21T17:06:35+00:00"
+        }
+    ],
+    "packages-dev": [
+        {
+            "name": "hamcrest/hamcrest-php",
+            "version": "v1.2.2",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/hamcrest/hamcrest-php.git",
+                "reference": "b37020aa976fa52d3de9aa904aa2522dc518f79c"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/hamcrest/hamcrest-php/zipball/b37020aa976fa52d3de9aa904aa2522dc518f79c",
+                "reference": "b37020aa976fa52d3de9aa904aa2522dc518f79c",
+                "shasum": ""
+            },
+            "require": {
+                "php": ">=5.3.2"
+            },
+            "replace": {
+                "cordoval/hamcrest-php": "*",
+                "davedevelopment/hamcrest-php": "*",
+                "kodova/hamcrest-php": "*"
+            },
+            "require-dev": {
+                "phpunit/php-file-iterator": "1.3.3",
+                "satooshi/php-coveralls": "dev-master"
+            },
+            "type": "library",
+            "autoload": {
+                "classmap": [
+                    "hamcrest"
+                ],
+                "files": [
+                    "hamcrest/Hamcrest.php"
+                ]
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "BSD"
+            ],
+            "description": "This is the PHP port of Hamcrest Matchers",
+            "keywords": [
+                "test"
+            ],
+            "time": "2015-05-11T14:41:42+00:00"
+        },
+        {
+            "name": "mockery/mockery",
+            "version": "0.9.7",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/padraic/mockery.git",
+                "reference": "4de7969f4664da3cef1ccd83866c9f59378c3371"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/padraic/mockery/zipball/4de7969f4664da3cef1ccd83866c9f59378c3371",
+                "reference": "4de7969f4664da3cef1ccd83866c9f59378c3371",
+                "shasum": ""
+            },
+            "require": {
+                "hamcrest/hamcrest-php": "~1.1",
+                "lib-pcre": ">=7.0",
+                "php": ">=5.3.2"
+            },
+            "require-dev": {
+                "phpunit/phpunit": "~4.0"
+            },
+            "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-master": "0.9.x-dev"
+                }
+            },
+            "autoload": {
+                "psr-0": {
+                    "Mockery": "library/"
+                }
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "BSD-3-Clause"
+            ],
+            "authors": [
+                {
+                    "name": "Pádraic Brady",
+                    "email": "padraic.brady@gmail.com",
+                    "homepage": "http://blog.astrumfutura.com"
+                },
+                {
+                    "name": "Dave Marshall",
+                    "email": "dave.marshall@atstsolutions.co.uk",
+                    "homepage": "http://davedevelopment.co.uk"
+                }
+            ],
+            "description": "Mockery is a simple yet flexible PHP mock object framework for use in unit testing with PHPUnit, PHPSpec or any other testing framework. Its core goal is to offer a test double framework with a succinct API capable of clearly defining all possible object operations and interactions using a human readable Domain Specific Language (DSL). Designed as a drop in alternative to PHPUnit's phpunit-mock-objects library, Mockery is easy to integrate with PHPUnit and can operate alongside phpunit-mock-objects without the World ending.",
+            "homepage": "http://github.com/padraic/mockery",
+            "keywords": [
+                "BDD",
+                "TDD",
+                "library",
+                "mock",
+                "mock objects",
+                "mockery",
+                "stub",
+                "test",
+                "test double",
+                "testing"
+            ],
+            "time": "2016-12-19T14:50:55+00:00"
+        },
+        {
+            "name": "tcz/phpunit-mockfunction",
+            "version": "v1.0.0",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/tcz/phpunit-mockfunction.git",
+                "reference": "87340f714620d7d6f8bb7fdd1f0ae50533acdcc3"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/tcz/phpunit-mockfunction/zipball/87340f714620d7d6f8bb7fdd1f0ae50533acdcc3",
+                "reference": "87340f714620d7d6f8bb7fdd1f0ae50533acdcc3",
+                "shasum": ""
+            },
+            "require": {
+                "ext-runkit": "*"
+            },
+            "type": "library",
+            "autoload": {
+                "classmap": [
+                    "PHPUnit/"
+                ]
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "description": "PHPUnit extension that uses runkit to mock PHP functions (both user-defined and system)",
+            "keywords": [
+                "mock",
+                "phpunit",
+                "runkit",
+                "testing",
+                "unit"
+            ],
+            "time": "2014-03-20T18:50:53+00:00"
+        }
+    ],
+    "aliases": [],
+    "minimum-stability": "stable",
+    "stability-flags": [],
+    "prefer-stable": false,
+    "prefer-lowest": false,
+    "platform": {
+        "php": ">=5.3.2"
+    },
+    "platform-dev": []
+}
diff --git a/lib/Innometrics/Profile.php b/lib/Innometrics/Profile.php
index af725b0..3aaf2dd 100644
--- a/lib/Innometrics/Profile.php
+++ b/lib/Innometrics/Profile.php
@@ -267,8 +267,8 @@ public function getSession ($sessionId) {
                 $session = $sess;
             }
         }
-        
-        return $session;         
+
+        return $session;
     }
 
     /**
@@ -352,7 +352,7 @@ protected function serializeSessions ($onlyChanges = false) {
     }
 
     /**
-     * Sort sessions by modifiedAt property
+     * Sort sessions by last event into the sessions
      * @return Profile
      */
     protected function sortSessions () {
diff --git a/lib/Innometrics/Session.php b/lib/Innometrics/Session.php
index d81b283..d573d31 100644
--- a/lib/Innometrics/Session.php
+++ b/lib/Innometrics/Session.php
@@ -32,12 +32,6 @@ class Session {
      */
     protected $createdAt = null;
 
-    /**
-     * Timestamp in ms when session was changed
-     * @var double
-     */
-    protected $modifiedAt = null;
-
     /**
      * Session data object
      * @var array
@@ -61,9 +55,9 @@ class Session {
      * @var bool
      */
     protected $dataDirty = false;
-    
+
     /**
-     * @param array $config equals to {id: id, section: sectionId, collectApp: collectApp, data: data, events: events, createdAt: timestamp, modifiedAt: modifiedAt }
+     * @param array $config equals to {id: id, section: sectionId, collectApp: collectApp, data: data, events: events, createdAt: timestamp }
      */
     public function __construct($config = array()) {
         $now = round(microtime(true) * 1000);
@@ -73,10 +67,9 @@ public function __construct($config = array()) {
         $this->setCollectApp(isset($config['collectApp']) ? $config['collectApp'] : null);
         $this->setSection(isset($config['section']) ? $config['section'] : null);
         $this->setCreatedAt(isset($config['createdAt']) ? $config['createdAt'] : $now);
-        $this->modifiedAt = isset($config['modifiedAt']) ? $config['modifiedAt'] : $now;
-        $this->initEvents(isset($config['events']) ? $config['events'] : array());        
+        $this->initEvents(isset($config['events']) ? $config['events'] : array());
     }
-    
+
     /**
      * Set session property and mark it as dirty
      * @param string $field Property to be set
@@ -89,8 +82,8 @@ protected function setField ($field, $value) {
             $this->setDirty();
         }
         return $this;
-    }    
-    
+    }
+
     /**
      * Set session id
      * @param string $id
@@ -99,7 +92,7 @@ protected function setField ($field, $value) {
     public function setId ($id) {
         return $this->setField('id', $id);
     }
-    
+
     /**
      * Set session application name
      * @param string $collectApp
@@ -108,7 +101,7 @@ public function setId ($id) {
     public function setCollectApp ($collectApp) {
         return $this->setField('collectApp', $collectApp);
     }
-    
+
     /**
      * Set session section name
      * @param string $section
@@ -117,7 +110,7 @@ public function setCollectApp ($collectApp) {
     public function setSection ($section) {
         return $this->setField('section', $section);
     }
-    
+
     /**
      * Set timestamp when session was created
      * Passed argument should be a number or Date instance
@@ -133,7 +126,7 @@ public function setCreatedAt ($date) {
         if (!is_numeric($date) && !($date instanceof \DateTime)) {
             throw new \ErrorException('Wrong date "' . $date . '". It should be an double or a DateTime instance.');
         }
-        
+
         if ($date instanceof \DateTime) {
             $ts = $date->getTimestamp();
             $date = $ts * 1000;
@@ -149,7 +142,7 @@ protected function isTimestampWithMilliseconds ($ts) {
         $nowLength = strval(microtime(true));
         return $tsLength >= $nowLength;
     }
-    
+
     /**
      * Update session data with values
      * Data is an array with key=>value pair(s).
@@ -159,7 +152,7 @@ protected function isTimestampWithMilliseconds ($ts) {
     public function setData ($data) {
         return $this->setField('data', array_merge($this->data, $data));
     }
-    
+
     /**
      * Set single value of session data
      * @param string $name
@@ -171,7 +164,7 @@ public function setDataValue ($name, $value) {
         $this->setDataDirty();
         return $this;
     }
-    
+
     /**
      * Get session id
      * @return string
@@ -179,7 +172,7 @@ public function setDataValue ($name, $value) {
     public function getId () {
         return $this->id;
     }
-    
+
     /**
      * Get session application name
      * @return string
@@ -187,7 +180,7 @@ public function getId () {
     public function getCollectApp () {
         return $this->collectApp;
     }
-    
+
     /**
      * Get session section name
      * @return string
@@ -195,7 +188,7 @@ public function getCollectApp () {
     public function getSection () {
         return $this->section;
     }
-    
+
     /**
      * Get timestamp in ms when session was created
      * @return double
@@ -203,15 +196,16 @@ public function getSection () {
     public function getCreatedAt () {
         return $this->createdAt;
     }
-    
+
     /**
      * Get timestamp in ms when session was changed
      * @return double
      */
     public function getModifiedAt () {
-        return $this->modifiedAt;
+        $lastEvent = $this->getLastEvent();
+        return $lastEvent ? $lastEvent->getCreatedAt() : $this->createdAt;
     }
-    
+
     /**
      * Get session data object
      * @return array
@@ -219,7 +213,7 @@ public function getModifiedAt () {
     public function getData () {
         return $this->data;
     }
-    
+
     /**
      * Get single value from session data object
      * @return mixed
@@ -252,9 +246,9 @@ public function addEvent ($event) {
 
         $events = $this->getEvents();
         $events[] = $event;
-        
+
         $this->events = $events;
-        
+
         $this->setDirty();
 
         return $event;
@@ -270,7 +264,7 @@ public function getEvent ($eventId) {
             return $event->getId() === $eventId;
         });
         $keys = array_keys($events);
-        return count($keys) ? $events[$keys[0]] : null;        
+        return count($keys) ? $events[$keys[0]] : null;
     }
 
     /**
@@ -300,16 +294,16 @@ public function getEvents ($eventDefinitionId = null) {
 
         return $events;
     }
-    
+
     /**
      * Check if session is valid (all required fields are present)
      * @return bool
      */
     public function isValid () {
-        return Validator::isSessionValid($this->serialize()) && 
+        return Validator::isSessionValid($this->serialize()) &&
             !!$this->getId() && !!$this->getSection() && !!$this->getCollectApp() && !!$this->getCreatedAt();
     }
-    
+
     /**
      * Serialize session from Session instance to array
      * @param bool $onlyChanges
@@ -322,15 +316,14 @@ public function serialize ($onlyChanges = false) {
         if (!$onlyChanges || $this->hasDataChanges()) {
             $data = $this->getData();
         }
-        
+
         return (object) array(
             'id' =>         $this->getId(),
             'section' =>    $this->getSection(),
             'collectApp' => $this->getCollectApp(),
             'data' =>       (object) $data,
             'events' =>     $events,
-            'createdAt' =>  $this->getCreatedAt(),
-            'modifiedAt' => $this->getModifiedAt()
+            'createdAt' =>  $this->getCreatedAt()
         );
     }
 
@@ -358,11 +351,6 @@ public function merge (Session $session) {
             throw new \ErrorException('Session IDs should be similar');
         }
 
-        // update last changed date
-        if ($session->modifiedAt > $this->modifiedAt) {
-            $this->modifiedAt = $session->modifiedAt;
-        }
-
         // merge data
         $this->setData($session->getData());
 
@@ -371,7 +359,7 @@ public function merge (Session $session) {
         foreach ($this->getEvents() as $event) {
             $eventsMap[$event->getId()] = $event;
         }
-        
+
         foreach ($session->getEvents() as $event) {
             $id = $event->getId();
             if (!isset($eventsMap[$id])) {
@@ -421,18 +409,18 @@ private function createEvent ($rawEventData) {
      */
     private function serializeEvents ($onlyChanges = false) {
         $eventsMap = array();
-        
+
         foreach ($this->getEvents() as $event) {
             if ($onlyChanges && !$event->hasChanges()) {
                 continue;
             }
-            
+
             $eventsMap[] = $event->serialize();
         }
-        
-        return $eventsMap;        
+
+        return $eventsMap;
     }
-    
+
     /**
      * Mark attribute as "dirty"
      * @return Session
@@ -441,7 +429,7 @@ protected function setDirty () {
         $this->dirty = true;
         return $this;
     }
-    
+
     /**
      * Resets "dirty" status
      * @return Session
@@ -449,14 +437,14 @@ protected function setDirty () {
     public function resetDirty () {
         $this->dirty = false;
         $this->dataDirty = false;
-        
+
         foreach ($this->getEvents() as $event) {
             $event->resetDirty();
         }
-        
+
         return $this;
     }
-    
+
     /**
      * Mark session data as "dirty"
      * @return Session
@@ -473,7 +461,7 @@ protected function setDataDirty () {
     public function hasChanges () {
         return !!$this->dirty || $this->hasDataChanges() || $this->hasEventsChanges();
     }
-    
+
     /**
      * Check if session has changes in data property
      * @return bool
@@ -492,8 +480,8 @@ protected function hasEventsChanges () {
                 return true;
             }
         }
-        
+
         return false;
     }
-    
+
 }
diff --git a/schema/attribute.json b/schema/attribute.json
index 4f9c7fe..1ac90e4 100644
--- a/schema/attribute.json
+++ b/schema/attribute.json
@@ -10,9 +10,6 @@
         },
         "data": {
             "type": "object"
-        },
-        "modifiedAt": {
-            "type": "number"
         }
     },
     "required": ["collectApp", "section", "data"]
diff --git a/schema/session.json b/schema/session.json
index 48495f0..0954308 100644
--- a/schema/session.json
+++ b/schema/session.json
@@ -57,10 +57,7 @@
         },
         "events": {
             "$ref": "events.json"
-        },
-        "modifiedAt": {
-            "type": "number"
         }
     },
-    "required": ["id", "createdAt", "collectApp", "section", "data", "events", "modifiedAt"]
+    "required": ["id", "createdAt", "collectApp", "section", "data", "events"]
 }
\ No newline at end of file
diff --git a/tests/EventTest.php b/tests/EventTest.php
index b0e4755..0d6c7dc 100644
--- a/tests/EventTest.php
+++ b/tests/EventTest.php
@@ -24,7 +24,7 @@ public function testShouldNotThrowErrorWhenCreateWithEmptyData () {
     public function testShouldGenerateOnlySomePropsByDefault () {
         $event = $this->createEvent();
         $this->assertStringMatchesFormat("%s", $event->getId());
-        $this->assertInternalType('double', $event->getCreatedAt());
+        $this->assertInternalType('float', $event->getCreatedAt());
         $this->assertInternalType('array', $event->getData());
         $this->assertEmpty($event->getDefinitionId());
         $this->assertFalse($event->isValid());
diff --git a/tests/Profile/ProfileTest.php b/tests/Profile/ProfileTest.php
index 7d59003..fa46647 100644
--- a/tests/Profile/ProfileTest.php
+++ b/tests/Profile/ProfileTest.php
@@ -5,7 +5,7 @@
 require_once('vendor/autoload.php');
 
 class ProfileTest extends Base {
-    
+
     protected $profileData = array(
         'id' => 'pid',
         'attributes' => array(
@@ -31,18 +31,16 @@ class ProfileTest extends Base {
                 'collectApp' => 'app1',
                 'section' => 'sec1',
                 'createdAt' => 1442476047267,
-                'modifiedAt' => 1442476047267,
                 'data' => array(
                     'data1' => 'value1'
                 ),
                 'events' => array()
-            ), 
+            ),
             array(
                 'id' => 'sid2',
                 'collectApp' => 'app2',
                 'section' => 'sec2',
                 'createdAt' => 1442476047267,
-                'modifiedAt' => 1442476047267,
                 'data' => array(),
                 'events' => array(
                     array(
@@ -54,19 +52,18 @@ class ProfileTest extends Base {
                         )
                     )
                 )
-            ), 
+            ),
             array(
                 'id' => 'sid3',
                 'collectApp' => 'app3',
                 'section' => 'sec3',
                 'createdAt' => 1442476047267,
-                'modifiedAt' => 1442476047267,
                 'data' => array(),
                 'events' => array()
             )
         )
     );
-    
+
     /**
      * TODO: should be splitted
      */
@@ -126,42 +123,42 @@ public function testShouldReturnSomeData () {
         $this->assertEquals(1, count($sessions));
         $session = $profile->getSession('sid');
         $this->assertEquals('value1', $session->getDataValue('name1'));
-    }    
-    
+    }
+
     public function testShouldNotThrowErrorOnEmptyConfig () {
         $this->assertInstanceOf('Innometrics\Profile', $this->createProfile());
         $this->assertInstanceOf('Innometrics\Profile', $this->createProfile(array()));
     }
-    
+
     public function testShouldBeInitedWithDefaultData () {
         $profile = $this->createProfile();
         $sessions = $profile->getSessions();
         $attributes = $profile->getAttributes();
-        
+
         $profileId = $profile->getId();
         $this->assertTrue(is_string($profileId));
         $this->assertEquals(32, strlen($profileId));
-        
+
         $this->assertTrue(is_array($sessions));
         $this->assertCount(0, $sessions);
-        
+
         $this->assertTrue(is_array($attributes));
         $this->assertCount(0, $attributes);
     }
-    
+
     public function testShouldUseIdFromConfig () {
         $profileId = 'pid';
         $profile = $this->createProfile(array(
             'id' => $profileId
         ));
-        
+
         $this->assertEquals($profileId, $profile->getId());
     }
-    
+
     public function testShouldProperlySerializeProfile () {
         $profileData = $this->profileData;
         $profile = $this->createProfile($profileData);
-        
+
         $serializedData = $profileData;
         foreach ($serializedData['attributes'] as $key => $item) {
             $item['data'] = (object) $item['data'];
@@ -170,29 +167,29 @@ public function testShouldProperlySerializeProfile () {
         }
         foreach ($serializedData['sessions'] as $key => $item) {
             $item['data'] = (object) $item['data'];
-            
+
             foreach ($item['events'] as $key2 => $item2) {
                 $item2['data'] = (object) $item2['data'];
                 $item2 = (object) $item2;
                 $item['events'][$key2] = $item2;
             }
-            
+
             $item = (object) $item;
             $serializedData['sessions'][$key] = $item;
         }
-        
+
         $this->assertEquals((object) $serializedData, $profile->serialize());
     }
-    
+
     public function testShouldSerializeOnlyChangedDataOfProfile () {
         $profileData = $this->profileData;
         $profile = $this->createProfile($profileData);
-        
+
         $profile->resetDirty();
         $this->assertFalse($profile->hasChanges());
-        
+
         $profile->getAttribute('test', 'app1', 'sec1')->setValue('babar');
-        
+
         $profile->getSession('sid1')->addEvent(array(
             'id' => 'a',
             'definitionId' => 'b',
@@ -201,9 +198,9 @@ public function testShouldSerializeOnlyChangedDataOfProfile () {
         $profile->getSession('sid2')->setDataValue('dd', 'bb');
 
         $this->assertTrue($profile->hasChanges());
-        
+
         $now = round(microtime(true) * 1000);
-        
+
         $this->assertEquals((object) array(
             'id' => 'pid',
             'attributes' => array(
@@ -221,7 +218,6 @@ public function testShouldSerializeOnlyChangedDataOfProfile () {
                     'collectApp' => 'app1',
                     'section' => 'sec1',
                     'createdAt' => 1442476047267,
-                    'modifiedAt' => 1442476047267,
                     'data' => (object) array(),
                     'events' => array(
                         (object) array(
@@ -237,19 +233,18 @@ public function testShouldSerializeOnlyChangedDataOfProfile () {
                     'collectApp' => 'app2',
                     'section' => 'sec2',
                     'createdAt' => 1442476047267,
-                    'modifiedAt' => 1442476047267,
                     'data' => (object) array(
                         'dd' => 'bb'
                     ),
                     'events' => array()
                 )
-            ) 
+            )
         ), $profile->serialize(true));
-    }    
-    
+    }
+
     public function testShouldReturnErrorIfProfileIsNotInstanceOfProfileWhileProfileMerging () {
         $profile = $this->createProfile();
-        
+
         foreach (array(null, true, array()) as $value) {
             try {
                 $profile->merge($value);
@@ -257,19 +252,19 @@ public function testShouldReturnErrorIfProfileIsNotInstanceOfProfileWhileProfile
                 $this->assertStringStartsWith('Argument 1 passed to Innometrics\Profile::merge() must be an instance of Innometrics\Profile', $e->getMessage());
             }
         }
-    }   
-    
+    }
+
     /**
      * @expectedException        ErrorException
      * @expectedExceptionMessage Profile IDs should be similar
-     */     
+     */
     public function testShouldReturnErrorIfIdsAreDifferentWhileProfileMerging () {
         $profile1 = $this->createProfile('pid1');
         $profile2 = $this->createProfile('pid2');
-        
+
         $profile1->merge($profile2);
-    }  
-    
+    }
+
     public function testShouldProperlyMergeDataFromProfileToOtherOne () {
         $profile1 = $this->createProfile(array(
             "id" => 'pid',
@@ -312,7 +307,7 @@ public function testShouldProperlyMergeDataFromProfileToOtherOne () {
                 )
             )
         ));
-        
+
         $profile2 = $this->createProfile(array(
             "id" => 'pid',
             "attributes" => array(
@@ -361,23 +356,23 @@ public function testShouldProperlyMergeDataFromProfileToOtherOne () {
                 )
             )
         ));
-        
+
         $profile1->merge($profile2);
-        
+
         $this->assertCount(3, $profile1->getAttributes());
         $this->assertEquals('baz', $profile1->getAttribute('foo', 'app1', 'sec1')->getValue());
-        
+
         $this->assertCount(3, $profile1->getSessions());
         $this->assertEquals(array(
             'test1' => 'e',
             'test2' => 'w'
         ), $profile1->getSession('sid2')->getData());
     }
-    
+
     public function testShouldBeChangedIfHasChangedAttribute () {
         $profile = $this->createProfile();
         $this->assertFalse($profile->hasChanges());
-        
+
         $profile->setAttribute(array(
             'collectApp' => 'web',
             'section' => 'sec',
@@ -386,11 +381,11 @@ public function testShouldBeChangedIfHasChangedAttribute () {
         ));
         $this->assertTrue($profile->hasChanges());
     }
-    
+
     public function testShouldBeChangedIfHasChangedSession() {
         $profile = $this->createProfile();
         $this->assertFalse($profile->hasChanges());
-        
+
         $profile->setSession(array(
             'collectApp' => 'web',
             'section' => 'sec',
@@ -398,7 +393,7 @@ public function testShouldBeChangedIfHasChangedSession() {
         ));
         $this->assertTrue($profile->hasChanges());
     }
-    
+
     public function testShouldNotChangedAfterResetDirty() {
         $profile = $this->createProfile(array(
             'attributes' => array(
@@ -412,9 +407,9 @@ public function testShouldNotChangedAfterResetDirty() {
             )
         ));
         $this->assertTrue($profile->hasChanges());
-        
+
         $profile->resetDirty();
         $this->assertFalse($profile->hasChanges());
     }
-    
+
 }
diff --git a/tests/Profile/SessionsTest.php b/tests/Profile/SessionsTest.php
index 772a866..69616d8 100644
--- a/tests/Profile/SessionsTest.php
+++ b/tests/Profile/SessionsTest.php
@@ -20,11 +20,11 @@ public function testShouldCreateSessionsFromConfig () {
                 )
             )
         ));
-        
+
         $sessions = $profile->getSessions();
-        
+
         $this->assertCount(1, $sessions);
-        
+
         $session = $sessions[0];
         $this->assertEquals($session->getCollectApp(), 'app');
         $this->assertEquals($session->getSection(), 'sec');
@@ -184,13 +184,27 @@ public function testShouldReturnLastSession () {
             'id'        => 'sid1',
             'collectApp'=> 'app1',
             'section'   => 'sec1',
-            'modifiedAt' => 100
+            'createdAt' => 1000000000000
         ]);
         $profile->setSession([
             'id'        => 'sid2',
             'collectApp'=> 'app2',
             'section'   => 'sec2',
-            'modifiedAt' => 50
+            'createdAt' => 1000000000001
+        ]);
+
+        $session = $profile->getLastSession();
+        $this->assertEquals('sid2', $session->getId());
+
+        $profile->getSession('sid1')->addEvent([
+            'id' => 'e1',
+            'definitionId' => 'b1',
+            'createdAt' => 1000000000004
+        ]);
+        $profile->getSession('sid2')->addEvent([
+            'id' => 'e2',
+            'definitionId' => 'b2',
+            'createdAt' => 1000000000003
         ]);
 
         $session = $profile->getLastSession();
diff --git a/tests/SessionTest.php b/tests/SessionTest.php
index 795e83e..cfd3eff 100644
--- a/tests/SessionTest.php
+++ b/tests/SessionTest.php
@@ -93,8 +93,7 @@ public function testShouldReceiveSerializeData () {
                     'createdAt' => $now
                 )
             ),
-            'createdAt' => $now,
-            'modifiedAt' => $now
+            'createdAt' => $now
         ));
 
         $this->assertEquals((object) array(
@@ -110,8 +109,7 @@ public function testShouldReceiveSerializeData () {
                     'createdAt' => $now
                 )
             ),
-            'createdAt' => $now,
-            'modifiedAt' => $now
+            'createdAt' => $now
         ), $session->serialize(), 'serialize test');
     }
 
@@ -131,8 +129,7 @@ public function testShouldBeCanWorkWithEvents () {
                     'createdAt' => $now
                 )
             ),
-            'createdAt' => $now,
-            'modifiedAt' => $now
+            'createdAt' => $now
         ));
 
         $session->setDataValue('name2', 'value2');