Threat Description

Sasser.F

Details

Aliases:Sasser.F, W32/Sasser.F, Worm.Win32.Sasser.a
Category: Malware
Type:
Platform: W32

Summary



Sasser.F is a minor modification of the Sasser.A worm. It shares all of its code and functionality, although it uses a different filename when copying itself into the system and a different mutex name.



Removal


Automatic action

Once detected, the F-Secure security product will automatically disinfect the suspect file by either deleting it or renaming it.

More

You may wish to refer to the Support Community for further assistance. You also may also refer to General Removal Instructions for a general guide on alternative disinfection actions.

Eliminating a Local Network Outbreak

If the infection is in a local network, please follow the instructions on this webpage:

Manual Disinfection

To manually disinfect an infected system, first apply the Microsoft patch MS04-011, then use Task Manager to kill the 'napatch.exe' process, then delete the file 'napatch.exe' from your Windows directory and reboot.

For step-by-step instructions, see Microsoft's site:http://www.microsoft.com/security/incident/sasser.asp#steps



Technical Details



Sasser.F is an unpacked, edited and repacked version of Sasser.A.For full details, please refer to the Sasser.A description.

System Infection

When the worm enters the system it creates a copy of itself in the Windows Directory as 'napatch.exe'. This copy is added to the Registry as

[SOFTWARE\Microsoft\Windows\CurrentVersion\Run]
  "napatch.exe" = "%WinDir%\napatch.exe"

To ensure that only one copy of the worm is running it creates a mutex named 'billgate'.






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