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.
Once detected, the F-Secure security product will automatically disinfect the suspect file by either deleting it or renaming it.
Eliminating a Local Network Outbreak
If the infection is in a local network, please follow the instructions on this webpage:
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.
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'.