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Published Dec 02, 2004 | Updated Sep 15, 2017

Worm:Win32/Nachi.B

Detected by Microsoft Defender Antivirus

Aliases: W32.Welchia.B.Worm (Symantec) WORM_NACHI.B (Trend Micro)

Summary

Win32/HLLW.Nachi.B is a network worm that targets Microsoft Windows 2000 and Windows XP. It propagates by exploiting several known vulnerabilities. It tries to download and apply security updates if it detects the operating system is a certain language version. It also tries to remove certain worms if they are on the infected system.
To manually recover from infection by Win32/HLLW.Nachi.B, perform the following steps:
  • Disconnect from the Internet
  • Remove the worm service
  • Delete the worm files from the computer
  • Delete the worm registry entry
  • Take steps to prevent re-infection

Disconnect from the Internet

To help ensure that your computer is not actively infecting other computers, 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.

Remove the worm service

Removing the worm service will help stop your computer from infecting other computers and resolve the crashing, restarting, and performance degradation issues that the worm causes.
To remove the worm service
  1. On the Start menu, click Control Panel.
  2. Double-click Administrative Tools.
  3. Double-click Services.
  4. Right-click the WksPatch service.
    5. Note: The Services tool does not display the actual service name WksPatch. The Services tool displays whatever name is contained in the registry key value:
    HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\WksPatch\DisplayName
  5. If the service is running, click Stop.
  6. Right-click the service again and click Properties.
  7. Under Startup Type, change the type to Disabled.

Delete the worm files from the computer

To delete the worm files from your computer
  1. Click Start, and click Run.
  2. In the Open field, type %windir%\system32\drivers
  3. Click OK.
  4. Click Name to sort files by name.
  5. Delete svchost.exe if it is in the list.
  6. On the Desktop, right-click the Recycle Bin and click Empty Recycle Bin.
  7. Click Yes.
If deleting files fails, use the steps in Remove the worm service to verify that the WksPatch service is not running.

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\System\CurrentControlSet\Services\WksPatch
  4. Click Delete and click Yes to delete the key.
  5. Close the Registry Editor.

Take steps to prevent re-infection

Do 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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