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Trojan:W32/Agent.AF

First posted on 23 July 2009.
Source: SecurityHome

Aliases :

Trojan:W32/Agent.AF is also known as Trojan:Win32/SMSer.B (Microsoft), Troj/SMSer-Gen (Sophos).

Explanation :

A trojan, or trojan horse, is a seemingly legitimate program which secretly performs other, usually malicious, functions. It is usually user-initiated and does not replicate.

Additional DetailsTrojan:W32/Agent.AF.A "locks" the machine and displays a message directing the user to send an SMS to a specified number in order to receive the password key to unlock the computer.

Agent.AF may be considered Ransomware as it hijacks the computer system and demands the user perform a specified action in order to regain control of the machine.

Agent.AF may be dropped on a computer by Trojan-Dropper:W32/Blocker.A.

Execution

Agent.AF installs to the Windows temp folder. All samples analyzed so far show that the file uses the filename


• donX.tmp

where X is a number.

The trojan then modifies the UserInit registry by adding a file path to the said registry so that it executes automatically.


• HKEY_LOCAL_MACHINESoftwareMicrosoftWindows NTCurrentVersionWinlogon
Userinit = %systemfolder%userinet.exe,
Note: The default value of this key is Userinit = %systemfolder%userinet.exe,

Activity

To take control of the computer, Agent.AF drop a batch file that forces the machine to reboot.

During reboot, the batch file "locks" the computer screen. At the same time, it disables several Windows shortcut key combinations to prevent the user from regaining control over the machine, including CTRL+ALT+DEL, Alt+F4 and others.

The trojan then displays the following message in a small window in the center:



The message directs the user to send an SMS containing a number key (generated by the malware) to the number 3649.

Last update 23 July 2009

 

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