MyDoom: Prevention and cure

MyDoom is a mass-mailing worm that masquerades as a test message. MyDoom (w32.mydoom@mm, also known as Novarg, Shimgapi, Shimg, and MiMail.r) takes advantage of the ZIP file format's ability to pass through email filters. It also uses Kazaa to spread. Within the first few hours, MyDoom spread quickly around the world. It affects only Windows users, not those using Macintosh, Linux, or Unix. Much of the worm's code is itself encrypted, and antivirus firms are still studying it. Because MyDoom spreads via email and could severely slow or shut down email servers with excess traffic, this worm rates a 7/10 on the ZDNet Virus Meter.

How it works
MyDoom arrives as email with the subject line "Mail Delivery System," "Test," or "Mail Transaction Failed". The body text reads: "The message contains Unicode characters and has been sent as a binary attachment." The attached files are one of the following:

document.zip
document.pif
doc.scr
message.pif
readme.exe
file.zip
message.zip
oia.zip
text.zip

When the worm is executed, MyDoom adds the following to the Windows/System subdirectory:

shimgapi.exe
taskmon.exe

If you are running the file-sharing program Kazaa, MyDoom will add a file named activation_crack.scr in this location: C:\Program files\Kazaa\My Shared Folder\.

The worm appears to install programs on infected computers, however, the programs themselves are encrypted. MyDoom is known to open Windows Notepad and display garbage text; it is also thought to be flooding Sco.com with a denial-of-service attack. In addition, the security company iDefense and McAfee are reporting that MyDoom opens port 3127 to listen for commands from a remote attacker.

Prevention
If you receive MyDoom, do not open the attached file. Delete the email.

Removal
Almost all antivirus software companies have updated their signature files to include this worm. This will stop the infection upon contact and in some cases will remove an active infection from your system. For more information, see Central Command, Computer Associates, F-Secure, McAfee, Norman, Sophos, Symantec or Trend Micro.