Summary

A new variant of Mimail worm - Mimail.M was found on 3rd of December, 2003.

The worm sends messages with seemingly personal content that promises pictures in a ZIP file which contains the worm instead.

Mimail.M also performs Distributed Denial-of-Service attacks against certain websites.

Disinfection

Manual disinfection of an Mimail.M infected computer consists of the following steps:

1, Remove the registry value [HKCU\Software\Microsoft\Windows\CurrentVersion\Run\NetMon]

2, Restart the computer

3, Delete '%WinDir%\netmon.exe' (where %WinDir% is the Windows Directory, typically c:\windows\ or c:\winnt)

Additional Details

The worm spreads in UPX packed form. The packed file is 10784 bytes in size. The unpacked worm body size is 23072 bytes and it was written in C language.

Email Spreading

Mimail.M arrives in emails with the following characteristics:

From: "Wendy" <some@email> To: recipient@somewhere Subject: Re[3] <random string>
Hello Greg,
I was shocked, when I found out that it wasn't you but your twin brother!!! That's amazing, you're as like as two peas. No one in bed is better than you Greg. I remember, I remember everything very well, that promised you to tell how it was, I'll give you a call today after 9.
<explicit content removed>
I'm so thankful to you, for acquainted me to your brother. I think we can do it on the next Saturday all three together? What do you think? O yes, as you wanted I've made a few pictures check them out in archive, I hope they will excite you, and you will dream of our new meeting...
Wendy.
Attachment: only_for_greg.zip
It has been reported that Mimail.M was seeded using the message above with an attachment called 'wendy.zip' which is 9903 bytes in size. The zip archive in the seed emails is password protected and the password is included at the end of the email message as well as a link to the archiver's download web page.

The worm collects email addresses from files on the infected computer. It recursively searches through the user's document folders and looks into all the files whose extension is not on the following list

"bmp" "jpg" "gif" "exe" "dll" "avi" "mpg" "mp3" "vxd" "ocx" "psd" "tif" "zip" "rar" "pdf" "cab" "wav" "com"
Using its own SMTP engine it sends emails with the malicious attachment. To find the SMTP server of the target email address the worm does an MX lookup using a predefined public DNS server.

System Infection

When started, Mimail.L first copies itself to the Windows Directory as 'netmon.exe'. This copy is added to the registry as

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

to make sure the worm is started when Windows starts.

The worm creates several temporary files in the Windows directory:

%WinDir%\msi2.tmp - worm packed into a ZIP file %WinDir%\nji2.tmp - copy of the worm %WinDir%\xjwu2.tmp - list of collected email addresses
Payload

As payload Mimail.M contains routines to perform Distributed Denial-of-Service attacks against the following sites:

darkprofits.ws darkprofits.cc darkprofits.net darkprofits.com

Detection

Detection in F-Secure Anti-Virus was published in update:

Version=2003-12-04_02

Technical Details: Gergely Erdelyi, December 3rd, 2003;

Description Updated: Katrin Tocheva, December 3rd, 2003;