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Published Nov 17, 2004 | Updated Sep 15, 2017

Worm:Win32/Sasser.F

Detected by Microsoft Defender Antivirus

Aliases: W32/Sasser.worm.f (McAfee) W32.Sasser.F.Worm (Symantec) WORM_SASSER.F (Trend Micro) W32/Sasser.F.worm (Panda) W32/Sasser-F (Sophos) Sasser.F (Norman)

Summary

Win32/Sasser.F.worm is a network worm that exploits the Local Security Authority Subsystem Service (LSASS) vulnerability fixed in Microsoft Security Update MS04-011. The worm targets Windows 2000 and Windows XP computers that do not have MS04-011 installed. Infected computers attempt to spread the worm to other unprotected computers by randomly scanning IP addresses and infecting vulnerable computers. 
To manually recover from infection by Win32/Sasser.F.worm, perform the following steps:
  • Disconnect from the Internet
  • End the worm process
  • Delete the worm files from your computer
  • Delete the worm registry entry
  • Restart your computer
  • Take steps to prevent re-infection

Disconnect from the Internet

To help ensure that your computer is not actively infecting other computers, you should disconnect it from the Internet before proceeding. Print this Web page or save a copy on your computer; then unplug your network cable and disable your wireless connection. You can reconnect to the Internet after completing these steps.

End the worm process

Ending the worm process will help stop your computer from infecting other computers as well as resolve the crashing, rebooting, and performance degradation issues caused by the worm.
To end the worm process
  1. Press CTRL+ALT+DEL once and click Task Manager.
  2. Click Processes and click Image Name to sort the running processes by name.
  3. Select the process napatch.exe, and click End Process.
  4. Repeat step 3 for any additional processes named napatch.exe, as well as any processes named <random number>_up.exe—for example 8843_up.exe.

Delete the worm files from the computer

After you end the worm process, you should delete the worm code from your computer.
To delete the worm files from the hard disk
  1. Click Start, and click Run.
  2. In the Open field, type %windir%
  3. Click OK.
  4. Click Name to sort files by name.
  5. If napatch.exe is in the list, delete it.
  6. Repeat step 1-4 for any processes in the %windir%\system32 directory named <random number>_up.exe—for example 8843_up.exe.
  7. On the Desktop, right-click the Recycle Bin and click Empty Recycle Bin.
  8. Click Yes.
This removes the worm code from your computer.
If deleting files fails, use the following steps to verify that napatch.exe is not running:
  1. Press CTRL+ALT+DEL once and click Task Manager.
  2. Click Processes and click Image Name to sort the running processes by name.
  3. Confirm that napatch.exe is not in the list.

Delete the worm registry entry

To delete the worm registry entry
  1. On the Start menu, click Run.
  2. Type regedit and click OK.
  3. In the left pane, navigate to the key: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
  4. In the right pane, right-click the value napatch.exe.
  5. Click Delete and click Yes to delete the value.
  6. Close the Registry Editor.

Restart your computer

To restart your computer
  1. On the Start menu, click Shut Down.
  2. Select Restart from the drop-down list and click OK.

Take steps to prevent re-infection

You should not reconnect your computer to the Internet until the computer is protected from re-infection. See the "Preventing Infection" section for more information.
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