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Published May 26, 2006 | Updated Sep 15, 2017

Worm:Win32/Chir.A@mm

Detected by Microsoft Defender Antivirus

Aliases: W32/Chir.a@MM (McAfee) WORM_CHIR.A (Trend Micro) Win32/Chir.10799 (CA)

Summary

Win32/Chir.A@mm is a mass-mailing worm. The worm sends a copy of itself as an e-mail attachment to e-mail addresses that it finds on the infected computer and remote shares. The worm runs when a user opens the e-mail attachment. On a computer that has not been patched for the Incorrect MIME Header vulnerability described in Microsoft Security Bulletin MS01-020, the attachment can open automatically under certain conditions.
To manually recover from infection by Win32/Chir.A@mm, follow these steps:
  1. Disconnect from the Internet.
  2. Restart your computer in safe mode.
  3. End the worm process.
  4. Delete the worm file.
  5. Delete the worm registry entry.
  6. Restart your computer.
  7. Take steps to prevent re-infection.

Disconnect from the Internet

To help ensure that your computer is not 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 your 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 and before Windows displays graphical output.
  3. From the Windows Advanced Options menu, select a safe mode option.

End the worm process

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 runouce.exe if it exists, and click End Process.

Delete the worm file

To delete the worm file:
  1. Click Start, and click Run.
  2. In the Open field, type the path to the Windows system folder. (For Windows NT-based systems such as Windows 2000 or Windows XP, the path to the system folder is %windir%\System32; for other Windows systems such as Windows 98 or Windows ME, the path is %windir%\System.)
  3. Click OK.
  4. Click Name to sort files by name.
  5. If runouce.exe is in the list, delete it.
  6. On the Desktop, right-click the Recycle Bin and click Empty Recycle Bin.
  7. Click Yes to confirm.
If deleting runouce.exe fails, follow these steps to verify that the corresponding process 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 runouce.exe is not in the list.

Delete the worm registry entry

Win32/Chir.A@mm creates an entry in the Windows registry that attempts to run the worm every time Windows starts. This entry should be deleted. To delete the 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 following value, if it exists: Runonce
  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

Do not reconnect your computer to the Internet until the computer is protected from re-infection. See the section on "How to Prevent Infection" for more information.
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