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Sasser.F


Aliases:


Sasser.F
W32/Sasser.F, Worm.Win32.Sasser.a

Malware

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.



Disinfection & Removal


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



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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