Threat Description



Aliases:MyDoom.AM, W32/Mydoom.AM@mm,


A new variant of MyDoom worm - Mydoom.AM, was found on January 25th, 2005. It spreads in e-mails with different subject and body texts, and attempts to spread in several P2P networks.


Automatic action

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


You may wish to refer to the Support Community for further assistance. You also may also refer to General Removal Instructions for a general guide on alternative disinfection actions.

Eliminating a Local Network Outbreak

If the infection is in a local network, please follow the instructions on this webpage:

Technical Details

The worm is a PE executable file 32768 bytes long packed with UPX file compressor. The unpacked file's size is over 76 KiB.

Installation to system

When run, the worm drops a file "Mes#wtelw" in temporary folder and writes some random data in the file. Then it opens this file in notepad as a decoy.

After the notepad is closed, the worm creates a mutex named "-=RTSW.Smash 0a2a0=-" and copies itself as

  • %Sysdir%\lsasrv.exe

where %Sysdir% is the Windows system directory. On default install of Windows XP, that is c:\Windows\system32. It also drops the following files:

  • %Sysdir%\version.ini
  • hserv.sys

version.ini contains supposedly the worm version number (0.20) and hserv.sys is encrypted data file containing web sites the worm contacts for instructions.

The worm installs the following registry keys:

  • [HKLM\Software\Microsoft\Windows\CurrentVersion\Run] "lsass" = %Sysdir%\lsasrv.exe
  • [HKLM\Software\Microsoft\Windows NT\CurrentVersion\Winlogon] "Shell" = "explorer.exe %Sysdir%\lsasrv.exe"

This will ensure that the worm will be started on next Windows startup.

Spreading in e-mails

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

  • txt
  • htm
  • sht
  • php
  • cgi
  • hta
  • htc
  • xht
  • stm
  • ssi
  • inc
  • jsp
  • xml
  • dlt
  • xsd
  • xst
  • rss
  • rdf
  • lbi
  • dwt
  • asa
  • asc
  • asm
  • csp
  • vbp
  • conf
  • tpl
  • jst
  • wml
  • vbs
  • edm
  • asp
  • dbx
  • tbb
  • adb
  • wab

The worm avoids sending e-mails to e-mail addresses that contain any of the following substrings:

  • avp
  • syma
  • icrosof
  • msn.
  • hotmail
  • panda
  • sopho
  • borlan
  • inpris
  • example
  • mydomai
  • nodomai
  • ruslis
  • .gov
  • gov.
  • .mil
  • foo.
  • berkeley
  • unix
  • math
  • bsd
  • mit.e
  • gnu
  • fsf.
  • google
  • kernel
  • linux
  • fido
  • usenet
  • iana
  • ietf
  • rfc-ed
  • sendmail
  • arin.
  • ripe.
  • isi.e
  • isc.o
  • secur
  • acketst
  • pgp
  • tanford.e
  • utgers.ed
  • mozilla

The subject of infected e-mails is selected from the following variants:

  • Good day
  • Do not reply to this email
  • hello
  • Mail Delivery System
  • Attention!!!
  • Mail Transaction Failed
  • Server Report
  • Status
  • Error

The body of the emails can one of the following:

Mail transaction failed. Partial message is available.
 The message contains Unicode characters and has been sent as a binary attachment.
 The message cannot be represented in 7-bit ASCII encoding and has been sent as a
 binary attachment.
 Attention! New self-spreading virus!
 Be careful, a new self-spreading virus called "RTSW.Smash"
 spreading very fast via e-mail and P2P networks. It's about
 two million people infected and it will be more. To avoid
 your infection by this virus and to stop it we provide you
 with full information how to protect yourself against it and
 also including free remover. Your can find it in the attachment.
 (c) 2004 Networks Associates Technology, Inc. All Rights Reserved

 New terms and conditions for credit card holders
 Here a new terms and conditions for credit card holders using
 a credit cards for making purchase in the Internet in the attachment.
 Please, read it carefully. If you are not agree with new terms and
 conditions do not use your credit card in the World Wide Web.
 Thank you, The World Bank Group
 (c) 2004 The World Bank Group, All Rights Reserved

 Thank you for registering at WORLDXXXPASS.COM
 All your payment info, login and password you can find in the
 attachment file. It's a real good choise to go to

 Attention! Your IP was logged by The Internet Fraud Complaint Center
 Your IP was logged by The Internet Fraud Complaint Center. There was
 a fraud attempt logged by The Internet Fraud Complaint Center from
 your IP. This is a serious crime, so all records was sent to the FBI.
 All information you can find in the attachment. Your IP was flagged
 and if there will be anover attemption you will be busted.
 This message is brought to you by the Federal Bureau of Investigation
 and the National White Collar Crime Center

The worm sends itself as an attachement, using one of the following names:

  • document
  • readme
  • doc
  • rules
  • file
  • data
  • docs
  • message
  • body

with one of the following extensions appended:

  • .bat
  • .cmd
  • .exe
  • .scr
  • .pif

Spreading in P2P networks

The worm will copy itself in folders used by Kazaa, Morpheus, iMesh, eDonkey and Limewire. It uses of the following filenames:

  • winamp5
  • icq2004-final
  • activation_crack
  • K-LiteCodecPack2.34a
  • dcom_patches
  • adultpaawds
  • winxp_patch
  • Ad-awarere
  • avpprokey
  • NeroBROM6.3.1.27
  • porno

with one of the following extensions appended:

  • .bat
  • .exe
  • .pif
  • .bat


The worm tries to contact several web sites and download instructions. These can instruct the worm to download and execute additional files.

The worm modifies the hosts file on infected computer so that domains belonging to Anti-Virus companies and other commercial sites are resolved to the IP address, disabling the domain. The following domains are affected:


It also tries to terminate several Firewall and Anti-Virus related processes.


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