Threat Descriptons



Category :


Type :


Aliases :

Mimail.M, W32/Mimail.m@mm, I-Worm.Mimail.m, I-Worm.Mimail.gen


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.


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

1, Remove the registry value


2, Restart the computer

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

A False Positive is when a file is incorrectly detected as harmful, usually because its code or behavior resembles known harmful programs. A False Positive will usually be fixed in a subsequent database update without any action needed on your part. If you wish, you may also:

  • Check for the latest database updates

    First check if your F-Secure security program is using the latest updates, then try scanning the file again.

  • Submit a sample

    After checking, if you still believe the file is incorrectly detected, you can submit a sample of it for re-analysis.

    Note: If the file was moved to quarantine, you need to collect the file from quarantine before you can submit it.

  • Exclude a file from further scanning

    If you are certain that the file is safe and want to continue using it, you can exclude it from further scanning by the F-Secure security product.

    Note: You need administrative rights to change the settings.

Technical 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:

It has been reported that Mimail.M was seeded using the message above with an attachment called '' 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


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


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


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