Name :	MyDoom.F
Category:	Malware
Type:	Virus
Platform:	Win32

A new variant of MyDoom worm - Mydoom.F was found on February 20th, 2004

It is functionally similar to the original variant but it
does not attack www.sco.com. Mydoom.F tries to perform a
Distributed Denial-of-Service attack on www.microsoft.com and
also www.riaa.com.

Mydoom.A description is available at:

http://www.f-secure.com/v-descs/novarg.shtml

Mydoom.B description is available at:

http://www.f-secure.com/v-descs/mydoom_b.shtml

Special Disinfection Tool


F-Secure has developed a special disinfection tool for this worm.
The tool will detect and remove an active Mydoom.F infection from
the computer.

The Mydoom removal tool can be downloaded in a ZIP file from:

ftp://ftp.f-secure.com/anti-virus/tools/f-mydoomf.zip

http://www.f-secure.com/tools/f-mydoomf.zip

The unpacked version is available from:

ftp://ftp.f-secure.com/anti-virus/tools/f-mydoomf.exe

http://www.f-secure.com/tools/f-mydoomf.exe

ftp://ftp.f-secure.com/anti-virus/tools/f-mydoomf.txt

http://www.f-secure.com/tools/f-mydoomf.txt

When copying itself, the worm will overwrite part of its executable with random data. Starting from 28000 bytes from its beginning it will write a 1 kB chunk of random data, making the file seem variable.

Some of the strings are scrambled using the same method as in the original
Mydoom, ROT13.

It will add an entry in the registry in:

[HKLM\Software\Microsoft\Windows\CurrentVersion\Run]

or, if failed in

[HKCU\Software\Microsoft\Windows\CurrentVersion\Run]

containing:

= %sysdir%\.exe

Email Propagation

The worm will compose emails with the following characteristics.

Subjects from the list:
(Some of these are also used by the Sober.C worm)


Message body is selected from:


Attachment names will be chosen from:


And one of the following extensions will be appended:


Payload


In addition to the Distributed Denial-of-Service attack the worm tries to delete several file types from the victim's hard drive such as pictures, movies and MS Office documents.

The worm's code in charge of that is the same that harvests e-mail addresses. It will check every drive from 'C' to 'Z', and for each of the folders on those, it will go through each file, performing the following actions:

-If the file is smaller the 40 bytes, it will skip it.

-It will extract the extension and match it against the following list:


If any of those is matched, it will attempt to extract any e-mail address
contained within.

-Next, the extension will be matched against:


The worm will delete the files with a given probability, so only a given
percentage of the occasions certain types of files will be deleted. The
following table gives those percentages:


Once the scan of the machine and its drives is finished, it will sleep for 32 seconds and start again.


Backdoor

This variant, as the previous ones, also drops a backdoor listening in port 1080.