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Published Dec 16, 2005 | Updated Sep 15, 2017

Worm:Win32/Dasher.A

Detected by Microsoft Defender Antivirus

Aliases: Dasher.A (F-secure)

Summary

Worm:Win32/Dasher.A is a network worm that can infect computers running Microsoft Windows 2000. The worm scans randomly-selected IP addresses to find computers that have a certain TCP port open. The worm exploits a Windows vulnerability when it finds the port open on a Windows 2000 computer that has not been patched with Microsoft Security Update MS05-051. Worm:Win32/Dasher.A then infects the computer in order to connect to a server and execute instructions from an attacker.
To recover manually from infection by Worm:Win32/Dasher.A, follow these steps:
  1. Disconnect from the Internet.
  2. Restart your computer in safe mode.
  3. End the worm processes.
  4. Delete the worm files.
  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 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 your computer in safe mode

To start your the 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 processes

To end the worm processes
  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 sqltob.exe if it exists, and click End Process.
  4. Repeat steps 2 and 3 for the following processes:
    sqlscan.exe
    sqlrep.exe
    sqlexp.exe

Delete the worm files

To delete the worm files
  1. Click Start, and click Run.
  2. In the Open field, type %windir%\temp
  3. Click OK.
  4. Click Name to sort files by name.
  5. Delete any of the following files if it is in the list:
    sqltob.exe
    sqlscan.exe
    sqlrep.exe
    sqlexp.exe
    result.txt
  6. On the Desktop, right-click the Recycle Bin and click Empty Recycle Bin.
  7. Click Yes to confirm.
If deleting any of the files fails, follow these steps to verify that none of the corresponding processes is 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 none of the processes is in the list.

Delete the worm registry entry

Worm:Win32/Dasher.A creates an entry in the Windows registry that attempts to run the worm automatically 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: Windows Update
  5. Click Delete and click Yes to delete the value.
  6. Close 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 "Preventing Infection" section for more information.
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