Threat Description



Aliases: Email-Worm.Win32.Mimail.c
Category: Malware
Type: Email-Worm
Platform: W32


This type of worm is embedded in an e-mail attachment, and spreads using the infected computer's e-mailing networks.


Automatic action

Once detected, the F-Secure security product will automatically disinfect the suspect file by either deleting it or renaming it.


Detailed instructions for F-Secure security products are available in the documentation found in the Downloads section of our Home - Global site.

You may also refer to the Knowledge Base on the F-Secure Community site for further assistance.

Technical Details

Email-Worm:W32/Mimail.C is a worm that propagates in infected e-mail message attachments. The worm is also capable of launching Denial of Service (DoS) attacks on certain websites.

The worm's file is a PE executable 12832 bytes long packed with UPX file compressor. The unpacked file's size is 28192 bytes.

Mimail.C was first found on 3 October, 2003.


Mimail.C is delivered in a ZIP archive file attachment to an e-mail message. The file uses the name PHOTOS.JPG.EXE.

The worm does not use any exploits to make its file start automatically on a recipient's system. The worm will infect a recipient's computer only when he/she unpacks the executable file from the archive and runs it.

When the worm's file is run, it registers itself as a service process and becomes invisible in Task List on Windows 9x systems. The the worm copies itself as NETWATCH.EXE file to Windows directory and creates a startup key for this file in System Registry:

  • [HKLM\Software\Microsoft\Windows\CurrentVersion\Run] "NetWatch32" = "%windir%\netwatch.exe"

where %windir% is Windows directory name.

Then the worm deletes the following files from Windows folder if they are present:

  • zip.tmp
  • exe.tmp
  • eml.tmp

After that the worm copies its file to Windows directory as EXE.TMP and creates a ZIP archive with the name ZIP.TMP. This ZIP archive contains the worm's copy with PHOTOS.JPG.EXE name.

The worm activates its payload and spreading theads if it can resolve the '' address.


The worm tries to perform a DoS attack on the following sites:


If the worm is widespread these sites may go down due to huge traffic amount generated by the worm.

Additionally the worm checks foreground windows and if it locates a window belonging to the certain application, the worm collects certain information from it and saves it to C:\TMPE.TMP file. Then this file is sent to e-mail addresses that are stored in an encrypted form in the worm's body.


The worm fakes the sender's e-mail address by composing it from 'james@' and the domain name of a recipient.

A malicious Mimail.C message has the following characteristics:

From: james@recipient_domain_name  Subject: Re[2]: our private photos  Body:  Hello Dear!,  Finally i've found possibility to right u, my lovely girl :)   All our photos which i've made at the beach (even when u're without ur bh:))   photos are great! This evening i'll come and we'll make the best SEX :)   Right now enjoy the photos.  Kiss, James.     Attachment:      

To collect victim's e-mail addresses the worm scans all files on an infected system's hard drive, except those with the following extensions:

  • bmp
  • jpg
  • gif
  • exe
  • dll
  • avi
  • mpg
  • mp3
  • vxd
  • ocx
  • psd
  • tif
  • zip
  • rar
  • pdf
  • cab
  • wav
  • com

The addresses are saved into the EML.TMP file located in Windows directory.

The worm tries to contact the recipient's SMTP server directly. For this purpose it tries to resolve the current user's DNSserver and search for SMTP server info for recipient's domain.


Mimail.C was distributed in an Inor variant. Inor is a VBS script that simply drops and runs a binary in c:\mware.exe (Mimail.C). The distributed VBS arrives in e-mail messages with the following characteristics:

Subject:    Body: This is the Postfix program at host    I'm sorry to have to inform you that the message returned    below could not be delivered to one or more destinations.    The message itself and all the other important information   are included into the attachment.  Attachment:  undelivered.hta  


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