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Published Nov 17, 2004 | Updated Sep 15, 2017

Worm:Win32/Randex.AB

Detected by Microsoft Defender Antivirus

Aliases: No associated aliases

Summary

Win32/Randex.AB.worm is a network worm that targets computers running certain versions of Microsoft Windows. The worm generates and scans IP addresses randomly to attempt to spread to writeable network shares that have weak passwords. The worm also has backdoor capabilities that allow attackers to control an infected computer through an IRC channel.
To manually recover from infection by Win32/Randex.AB.worm, perform the following steps:
  1. Disconnect from the Internet.
  2. Restart the computer in safe mode.
  3. End the worm process.
  4. Delete the worm files from the computer.
  5. Delete the worm registry entries.
  6. Restart your computer.
  7. Scan network shares with an antivirus program. 
  8. Take steps to prevent re-infection.

Disconnect from the Internet

To 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.

Restart the computer in safe mode

To start your computer in safe mode
  1. Remove all floppy disks and CDs from your computer, and then restart your computer.
  2. When prompted, press F8. If Windows starts without displaying the Please select the operating system to start menu, restart your computer. Press F8 after the firmware POST process completes, but before Windows displays graphical output.
  3. From the Windows Advanced Options menu, select a safe mode option.

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 each process called msnwun.exe, and then click End Process.

Delete the worm files from the computer

To delete the worm files from the computer
  1. Click Start, and then click Run.
  2. In the Open field, type %Windir%\System32
  3. Press Enter.
  4. Click the Name column to sort files by name.
  5. If the file msnwun.exe is in the list, delete it.
If deleting files fails, use the following steps to verify that msnwun.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 msnwun.exe is not in the list.

Delete the worm registry entries

Win32/Randex.AB.worm creates several entries in the Windows registry. These entries attempt to run the worm every time your computer restarts. The worm also adds the names of some security applications to the DisallowRun or RestrictRun entries. These entries should be deleted.
To delete the worm registry entries
  1. On the Start menu, click Run.
  2. For Windows 9x or Windows ME, type command and click OK.
    For Windows 2000, Windows NT, or Windows XP, type cmd and click OK. 
  3. At the command prompt, type copy %Windir%\regedit.exe regedit.com|regedit.com
  4. In the left pane of Registry Editor, navigate to the key:
    HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
  5. In the right pane, right-click the value:
    Microsoft Windows Updates = msnwun.exe
  6. Select Delete and click Yes to delete the value.
  7. Repeat step 4 to step 6 for the following two registry keys:
    HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\RunServices
    HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
  8. 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.

Scan network shares with an antivirus program

  1. On the Start menu, click Run.
  2. Type cmd and click OK.
  3. Type net share
  4. Run an antivirus program to scan the resource locations of listed shares.

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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