Threat Description





A new variant of Zafi worm - Zafi.F is spreading. While the original Zafi.A uses only Hungarian, the Zafi.F spreads in email in English, Italian, Spanish, Russian, Swedish and several other languages. The worm sends itself in infected messages attached as .pif, .cmd, .bat, .com or .zip file. This variant of Zafi also spreads in P2P networks. It can display a decoy message in message box saying "Image format error!"


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.

Technical Details

Zafi.F spreads in FSG! packed form which is 16770 bytes in size. The body unpacks to around 30 KiB of hand-written assembly code.

System Infection

When Zafi.F is started it copies itself to the Windows System Directory with a name "AntiVirus Update.exe". This file is added to the following registry key:

 "Zi5" = "%System%\AntiVirus Update.exe" 

Zafi.F creates a mutex named "Zi5" for making sure that only one copy of the worm is run at the same time.

Zafi.F enumerates all the directories in the system and copies itself as either 'Adobe Acrobat 8.0 Pro.exe' or 'Windows Update Crack.exe' to the ones that contain 'shar', 'uploa' or 'musi' in their name.

Email Propagation

Zafi.F looks into the Windows Address Book and different files and tries to gather email addresses. Files with the following extensions are checked:

  • dbx
  • asp
  • txt
  • htm
  • mbx
  • wab
  • php
  • sht
  • adb
  • tbb
  • inb
  • pmr
  • fpt
  • eml

Using its own SMTP engine the worm sends messages with infected attachments in many different languages. It can use different SMTP relays for sending its messages depending on the language.

For email addresses in the following domains the worms sends messages in the respective languages:

.hu .sp .se .de .at .ch .nl .fr .it .es .mx .ru 

Following text is an example of english message:

From: M. Christina 
 Subject: msn photo ecard 
 commercial ecard :)) 

Sender name is used as a fallback if the email address doesn't have it.

Other language versions are as follows:

From: Szalai Bernadett 
 Subject: legszexibb megasztar foto! 
 szavazz ra te is! 
 From: N. Fernandez 
 Subject: broma :)) 
 humor :)) 
 From: H. Andersson 
 Subject: rolig reklam :)) 
 haha - rolig :))  
 From: H. Maria 
 Subject: witzig reklame :)) 
 witzig bild :D
 From: R. Cornel 
 Subject: grappig beeld :)) 
 een grappig reclame :D  
 From: B. Martin 
 Subject: blague :)) 
 humour - reclame :)) 
 From: R. Antonio 
 Subject: scherzo :)) 
 comico quadro :))
 From: N. Fernandez 
 Subject: broma :)) 
 humor :))
 From: D. Alexej 
 The body message is  
 ImageFormat: 640x480 
 ImageSize: 16Kb 
 Message: you need to see this :)) 
 AV-Control: MSN Mail: +++ No Virus 

The actual attachment is a ZIP file with name composed of the following words:

  • reklam
  • megasztar
  • humor
  • reklame
  • reclame
  • funny
  • commercial

Inside the ZIP file, there is a copy of the worm using one of the following file extensions:

  • .bat
  • .cmd
  • .com
  • .pif

Here's a screenshot of English message:

The worm does not send emails to addresses that contain any of these strings:

  • admi
  • bitde
  • contact@
  • eset
  • -faq
  • google
  • help
  • hotmai
  • info
  • linux
  • kasper
  • mcafe
  • micro
  • msn
  • nod3
  • panda
  • sales
  • secur
  • service
  • soft
  • sopho
  • subsc
  • suppor
  • support
  • symant
  • test
  • trend
  • use
  • webm
  • win
  • www


Zafi.F terminates any application that has the words 'firewall' or 'virus' in it. These files are overwritten with a copy of the worm.

Several Windows tools, like Task Manager, Registry Editor are disabled when the worm is active. Zafi.F opens these files with exclusive locking to prevent anything else from opening them.

Zafi.F has a backdoor that listens on port 2121. The worm can upload and execute file using the backdoor.


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