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Published Aug 15, 2005 | Updated Apr 16, 2011

Worm:Win32/Zotob.C

Detected by Microsoft Defender Antivirus

Aliases: Zotob.C (Trend Micro) W32/Zotob.worm.c (McAfee) W32.Zotob.C (Symantec) W32/Zotob.C (F-secure) W32/Zotob-C (Sophos) Zotob.C (CA)

Summary

Worm:Win32/Zotob.C is a network worm that exploits the Plug-and-Play vulnerability fixed in Microsoft Security Bulletin MS05-039. The worm targets computers running Microsoft Windows 2000 that do not have MS05-039 installed. The worm can also infect computers running other versions of Windows operating systems if it is delivered through e-mail, instant messaging, or other routes.
To manually recover from infection by Worm:Win32/Zotob.C, follow these steps:
  1. Install security update MS05-039.
  2. Disconnect from the Internet.
  3. End the worm process.
  4. Delete the worm files from your computer.
  5. Delete the worm registry entries.
  6. Clean the system host file.
  7. Restart your computer.
  8. Take steps to prevent re-infection.
  9. Run an antivirus scan.
Install security update MS05-039
To install MS05-039 using Windows Update
  1. Go to the Windows Update Web site at windowsupdate.microsoft.com.
  2. On the Windows Update site, click Scan for Updates. Windows Update scans your computer and returns a list of critical updates, including service packs.
  3. In the Pick updates to install list, click Critical Updates and Service Packs. Windows Update creates a list of the updates appropriate for your computer, including MS05-039 if it is not installed. Critical updates are selected for download automatically.
  4. Click Review and install updates, and then click Install Now. You may need to restart your computer after installing the updates.
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.
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 per.exe, and click End Process.
Delete the worm files from your computer
To delete the worm files from your computer
  1. Click Start, and click Run.
  2. In the Open field, type the name of the system folder, for example, C:\Winnt\system32\
  3. Click OK.
  4. Click Name to sort files by name.
  5. If per.exe is in the list, delete it.
  6. On the Desktop, right-click the Recycle Bin and click Empty Recycle Bin.
  7. Click Yes.
If deleting the files fails, follow these steps to verify that per.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 per.exe is not in the list.
Delete the worm registry entries
Worm:Win32/Zotob.C creates entries in the Windows registry that attempt to run the worm every time your computer restarts. These entries should be deleted.
To delete the worm registry entries
  1. On the Start menu, click Run.
  2. Type regedit and click OK.
  3. In the left pane, navigate to the key: HKLM\Software\Microsoft\Windows\CurrentVersion\Run
    In the right pane, right-click the following value, if it exists:
    WINDOWS SYSTEM
  4. Click Delete and click Yes to delete the values.
  5. Repeat steps 3-4 for HKLM\Software\Microsoft\Windows\CurrentVersion\RunServices.
  6. Close Registry Editor.
Clean the system host file
The worm makes changes to the system host file to prevent access to certain Web sites.
To clean the system host file.
  1. On the Start menu, click Run.
  2. Type notepad.exe and click OK.
  3. On the File menu, click Open…
  4. In the File name text box, type the name of the Windows directory folder and \system32\drivers\etc\hosts, for example, C:\winnt\system32\drivers\etc\hosts.
  5. Search for text that begins with "Botzor2005 Made By…"
  6. Select this text and all text that follows. Delete the selected text and save the file.
  7. Close Notepad.
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
Do not reconnect your computer to the Internet until the computer is protected from re-infection. See the "Preventing Infection" section for more information.
Run an antivirus scan
To detect and remove this threat and other malicious software that may have been installed, run a full-system scan with an up-to-date antivirus product such as Microsoft Security Essentials, or the Microsoft Safety Scanner. For more information about using antivirus software, see http://www.microsoft.com/security/antivirus/av.aspx.
Additional remediation instructions for Worm:Win32/Zotob.C
This threat may make lasting changes to a computer’s configuration that are NOT restored by detecting and removing this threat. For more information on returning an infected computer to its pre-infected state, please see the following article/s: 
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