-- Update March 11, 2004 --
The risk assessment of this threat was lowered to Low-Profiled due to a decrease in prevalence.
--Update 17th Febuary, 2004
The risk assessment was lowered to Medium due to a decrease in prevalence.
--Update 12th Febuary, 2004
A new variant of this virus has been discovered. The file size is 24,048 bytes (petite packed). It is proactively detected as W32/Mydoom.a@MM using the above specified DATs. The functionality of this new variant is similar to the .a variant, except that the body of the email it sends out may contain the following:
- ROFL HELLO SAM HOWS UPZ. Partial message is available
This is a mass-mailing and peer-to-peer file-sharing worm that bears the following characteristics:
- contains its own SMTP engine to construct outgoing messages
- contains a backdoor component (see below)
- contains a Denial of Service payload
Mydoom only infects systems running Microsoft Windows.
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).
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:
(Spoofed email sender)
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.
(Varies, such as)
- Server Report
- Mail Transaction Failed
- Mail Delivery System
(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.
(varies [.bat, .exe, .pif, .cmd, .scr] - often arrives in a ZIP archive) (22,528 bytes)
- examples (common names, but can be random)
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:
When this file is run (manually), it copies itself to the WINDOWS SYSTEM directory as taskmon.exe
(Where %Sysdir% is the Windows System directory, for example C:\WINDOWS\SYSTEM)
It creates the following registry entry to hook Windows startup:
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:
\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:
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
If the worm is run after February 1st 16:09:18 (UTC), it 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 after February 12th 02:28:57 (UTC) , and thereafter the worm's only behavior is to continue listening on TCP port 3127 (or up to 3198). Due to a bug in the code, the DoS attack will fail to start 75% of the time.
The denial of service executes by creating 64 threads each of which makes a HTTP GET request from random ports on the infected machines to port 80 of www.sco.com.