• contains its own SMTP engine to construct outgoing messages
• contains a backdoor component (see below)
• contains a Denial of Service payload

If you think that you may be infected with Mydoom, and are unsure how to check your system, you may download the Stinger tool to scan your system and remove the virus if present.  This is not required for McAfee users as McAfee products are capable of detecting and removing the virus with the latest update. (see the removal instructions below for more information).

Note: Receiving an email alert stating that the virus came from your email address is not an indication that you are infected as the virus often forges the from address. 

The virus arrives in an email message as follows:

From: (Spoofed email sender)
Subject: (Varies, such as)

• Error
• Status
• Server Report
• Mail Transaction Failed
• Mail Delivery System
• hello
• hi

Body:  (Varies, such as) 

• The message cannot be represented in 7-bit ASCII encoding and has been sent as a binary attachment.
• The message contains Unicode characters and has been sent as a binary attachment.
• Mail transaction failed. Partial message is available.

Attachment: (varies [.bat, .exe, .pif, .cmd, .scr] - often arrives in a ZIP archive) (22,528 bytes)

• examples (common names, but can be random)
• doc.bat
• document.zip
• message.zip
• readme.zip
• text.pif
• hello.cmd
• body.scr
• test.htm.pif
• data.txt.exe
• file.scr

In the case of two file extensions, multiple spaces may be inserted as well, for example:

• document.htm  (many spaces)  .pif

The icon used by the file tries to make it appear as if the attachment is a text file:

Note: Do not assume that the sender address is an indication that the sender is infected.  Additionally you may receive alert messages from a mail server that you are infected, which may not be the case.

When this file is run (manually), it copies itself to the WINDOWS SYSTEM directory as taskmon.exe

•  %SysDir%\taskmon.exe

(Where %Sysdir% is the Windows System directory, for example C:\WINDOWS\SYSTEM)

It creates the following registry entry to hook Windows startup:

• HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\
  CurrentVersion\Run "TaskMon" = %SysDir%\taskmon.exe

The virus uses a DLL that it creates in the Windows System directory:

•  %SysDir%\shimgapi.dll (4,096 bytes)

This DLL is injected into the EXPLORER.EXE upon reboot via this registry key:

• HKEY_CLASSES_ROOT\CLSID\{E6FB5E20-DE35-11CF-9C87-00AA005127ED}\InProcServer32 "(Default)" = %SysDir%\shimgapi.dll

The virus will not replicate on the 12th February or later (although the DLL will still be installed).

Peer To Peer Propagation
The worm copies itself to the KaZaa Shared Directory with the following filenames:

• nuke2004
• office_crack
• rootkitXP
• strip-girl-2.0bdcom_patches
• activation_crack
• icq2004-final
• winamp

Remote Access Component
The worm (this functionality is in the dropped DLL) opens a connection on TCP port 3127 (if that fails it opens next available port up to port 3198). The worm can accept specially crafted TCP transmissions.

• On receipt of one kind of such a transmission it will save the embedded binary into a temporary file and execute it. Then the temporary file is deleted.
• On receipt of another kind it can relay TCP packets thus providing IP spoofing capabilities (possibly to facilitate SPAM distribution)

Denial of Service Payload
On the first system startup on February 1st or later, the worm changes its behavior from mass mailing to initiating a denial of service attack against www.sco.com. This denial of service attack will stop on the first system startup of February 12th or later, and thereafter the worm's only behavior is to continue listening on TCP port 3127

The mailing component harvests address from the local system.  Files with the following extensions are targeted:

• wab
• adb
• tbb
• dbx
• asp
• php
• sht
• htm
• txt
• pl

The worm avoids certain address, those using the following strings:

• .gov
• .mil
• abuse
• acketst
• arin.
• avp
• berkeley
• borlan
• bsd
• example
• fido
• foo.
• fsf.
• gnu
• google
• gov.
• hotmail
• iana
• ibm.com
• icrosof
• ietf
• inpris
• isc.o
• isi.e
• kernel
• linux
• math
• mit.e
• mozilla
• msn.
• mydomai
• nodomai
• panda
• pgp
• rfc-ed
• ripe.
• ruslis
• secur
• sendmail
• sopho
• syma
• tanford.e
• unix
• usenet
• utgers.ed

Additionally, the worm contains strings, which it uses to randomly generate, or guess, email addresses. These are prepended as user names to harvested domain names:

• sandra
• linda
• julie
• jimmy
• jerry
• helen
• debby
• claudia
• brenda
• anna
• alice
• brent
• adam
• ted
• fred
• jack
• bill
• stan
• smith
• steve
• matt
• dave
• dan
• joe
• jane
• bob
• robert
• peter
• tom
• ray
• mary
• serg
• brian
• jim
• maria
• leo
• jose
• andrew
• sam
• george
• david
• kevin
• mike
• james
• michael
• john
• alex

Finally the virus sends itself via SMTP - constructing messages using its own SMTP engine.  The worm guesses the recipient email server, prepending the target domain name with the following strings:

• mx.
• mail.
• smtp.
• mx1.
• mxs.
• mail1.
• relay.
• ns.

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