Trojan-Downloader.Win32.Agent.zf

Technical Details

This memory resident malicious program is a Windows PE EXE file written in Microsoft Visual C++. The file is 7013 bytes in size. However, file size varies significantly from variant to variant.

Payload

Once launched, the Trojan copies itself to the Windows root directory as SERVICES.EXE and then launches this file for execution.

The original file will then be deleted.

The Trojan also creates the following keys in the system registry:

The SERVICES.EXE which is launched in a separate stream constantly creates the following values in the system registry:

This ensures that the Trojan file will be launched automatically each time Windows is rebooted on the victim machine.

It is impossible to terminate the Trojan process as Windows believes it to be a system process (%system%\services.exe — this is due to the fact that the name of the Trojan process is identical to that launched on the system.).

The Trojan is also capable of downloading files from the Internet and launching them on the victim machine.

Removal instructions

Manual removal:

1. Create a c:\rescue.bat file which contains the following strings:
   @echo off
   :try
   del C:\WINDOWS\SERVICES.EXE
   if exist C:\WINDOWS\SERVICES.EXE goto try
2. Modify the following system registry entry: from
   [HKLM\System\CurrentControlSet\Services\Eventlog]
    "ImagePath"="%SystemRoot%\system32\services.exe"
   to
    "ImagePath"="C:\rescue.bat"

   Doing this ensures that rescue.bat will be launched instead of the Event Log system servcie.

3. Reboot the computer. The Trojan will be deleted once the system has been rebooted.
4. Restore the original ImagePath value:
   [HKLM\System\CurrentControlSet\Services\Eventlog]
    "ImagePath"="%SystemRoot%\system32\services.exe"
5. Delete the following keys from the system registry:

   [HKLM\Software\Microsoft\Serenta]

   [HKLM\Software\Microsoft\Windows\CurrentVersion\Run]
    "SERVICES.EXE"="%Windir%\SERVICES.EXE"

6. Modify the following parameters:
   [HKLM\Software\Microsoft\Windows NT\CurrentVersion\Winlogon]
    "Shell"="Explorer.exe %Windir%\SERVICES.EXE"
   to:
    "Shell"="Explorer.exe"
    "Userinit"="C:\WINDOWS\system32\userinit.exe,,%Windir%\SERVICES.EXE"
   to:
    "Userinit"="C:\WINDOWS\system32\userinit.exe"
7. Update your antivirus databases and perform a full scan of your computer (download a trial version of Kaspersky Anti-Virus).