ALIAS:	W32/Sasser.F, Worm.Win32.Sasser.a
SIZE:	74752

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.

Automatic Disinfection

Allow F-Secure Anti-Virus to disinfect the relevant files.

For more general information on disinfection, please see Removal Instructions.

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

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'.