Threat Descriptons



Category :


Type :


Aliases :

MyDoom.AC, .Mydoom.w, W32/Mydoom.AC@mm


A new variant of MyDoom worm - Mydoom.AC, was found in the middle of September 2004. This worm variant can spread in emails as a fake FlashEcard virtual postcard.


Based on the settings of your F-Secure security product, it will either move the file to the quarantine where it cannot spread or cause harm, or remove it.

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 is a PE executable file 23040 bytes long packed with PECompact and PECBundle file compressors and modified by PE_Patch. The unpacked file's size is over 61 kilobytes.

Installation to system

When run, the worm starts Internet Explorer and goes to '' website as a disguise.

Then the worm creates a mutex 'holla_back_bitches', copies itself as SYSHOSTS.EXE to Windows System Directory and creates a startup key for that file in System Registry:

  • [HKCU\Software\Microsoft\Windows\CurrentVersion\Run] "MS Updates" = "%WinSysDir%\syshosts.exe"

where "%WinSysDir%" represents Windows System directory.

Spreading in emails

The worm spreads by sending its infected attachment to all email addresses found on an infected computer. The worm looks for email addresses in Windows Address Book and in the files with the following extensions:

  • txt
  • htm
  • html
  • sht
  • php
  • eml
  • msg
  • asp
  • dbx
  • tbb
  • adb
  • pl
  • wab

The worm avoids sending emails to email addresses that contain any of the following substrings:

  • icrosof
  • syma
  • msn
  • hotmail
  • anda
  • opho
  • borlan
  • npris
  • xample
  • mydom
  • @domai
  • ruslis
  • .gov
  • .gov
  • .mil
  • @foo
  • berkeley
  • unix
  • math
  • bsd
  • mit.e
  • gnu
  • fsf.
  • ibm
  • oogle
  • kernel
  • linux
  • fido
  • senet
  • @ian
  • ripe
  • isi.e
  • arin.
  • rfc-ed
  • isc.o
  • ecur
  • acketst
  • pgp
  • tanford.e
  • utgers.ed
  • ample
  • info
  • root@
  • ostmaster@
  • ebmaster@
  • you
  • ugs@
  • ating@
  • ontact@
  • soft
  • rivacy
  • ervice
  • help
  • ubmit@
  • feste
  • cert
  • page
  • upport
  • ntivi
  • istser
  • ertific
  • ccoun
  • spm
  • Spam
  • SPAM
  • spam
  • abuse
  • cafee
  • @messagelab
  • @avp
  • kasp
  • winzip
  • winrar
  • pdate
  • irus
  • ahoo
  • buse@
  • sale

The subject of infected emails is selected from the following variants:

  • album
  • You've got a Virtual Postcard!

The body text of infected emails is selected from the following variants:

my pics...*sexy*. Heheh! ;)


You have just received a new postcard from!


To pick up your postcard follow this web address
or click the attached link.
We hope you enjoy your postcard, and if you do, please
take a moment to send a few yourself!

(Your message will be available for 30 days.)

Please visit our site for more information.

The worm can send itself as an executable attachment or in a ZIP archive with one of the following names:

  • photos_album

The extension of an infected file can be any of the following:

  • .scr
  • .html.scr

The worm fakes the sender's address. It uses the following list of names to compose the fake address:

  • Jennifer
  • Barbara
  • Linda
  • Susan
  • Eric
  • Kevin
  • Mary
  • Robert
  • John
  • Maria
  • Alex
  • Pamela
  • Anna
  • Andrew
  • Fred
  • Jack
  • James
  • Julie
  • Debby
  • Claudia
  • Matt
  • Brent

It uses the following list of domain names to compose the fake address:


Killing processes

The worm kills processes if it finds any of the following substrings in their names:

  • regedit
  • task
  • msconfig
  • AV
  • MC
  • Av
  • Mc
  • av
  • mc
  • IEFrame
  • nti
  • iru
  • ire
  • cc
  • ecu
  • can
  • scn
  • KV
  • fr


After December 1st, 2004, 01:01:01 the worm shuts down Windows on an infected computer after its file is started. As a result a user can not log in any more.

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