Threat Description

Worm:​W32/Klez.H

Details

Aliases:Worm:​W32/Klez.H
Category:Malware
Type:Worm
Platform:W32

Summary



A standalone malicious program which uses computer or network resources to make complete copies of itself. May include code or other malware to damage both the system and the network.



Removal


Automatic action

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

More

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.

For more general information on disinfection, please see Removal Instructions.

Video: Klez Removal Help

We have produced a video showing step-by-step how to get rid of the Klez worm. View the video at: http://www.f-secure.com/virus-info/video/klez.ram

Note: The video requires RealPlayer to view. You may download RealPlayer from: http://www.real.com/player/index.html?lang=en



Technical Details



This new version of the Klez worm has been found from various parts of Asia on April 17th, 2002. A week after its discovery Klez.H is globally spread. This worm, like its previous versions sends e-mail messages with randomly named attachments and subject fields.

The Klez.H variant it quite close to previous variants Klez.E, F and G.

Here is a screenshot showing what Klez messages could look like:

F-Secure Virus Research Team found the following differences in Klez.H variant compared to its previous versions:

  • There's no payload routine.
  • The .PDF extension was added to the list of extensions that the worm uses to make a double-extension name for its file.
  • The worm sometimes uses social engineering approach in its spreading and sends the following message with its own file attached :
    Subject: Worm Klez.E immunity
    Body: 
    Klez.E is the most common world-wide spreading worm.It's very
    dangerous by corrupting your files.
    Because of its very smart stealth and anti-anti-virus
    technic,most common AV software can't detect or clean it.
    We developed this free immunity tool to defeat the malicious
    virus.
    You only need to run this tool once,and then Klez will never
    come into your PC.
    NOTE: Because this tool acts as a fake Klez to fool the real
    worm,some AV monitor maybe cry when you run it.
    If so,Ignore the warning,and select 'continue'.
    If you have any question,please mail to me.
    
    The 'mail to me' is represented as a link to the sender's e-mail address. Note that this address is not always the real sender's address.
  • The worm contains a new text message from its author. This text is never displayed:
    Win32 Klez V2.01 & Win32 Foroux V1.0
    Copyright 2002,made in Asia
    About Klez V2.01:
    1,Main mission is to release the new baby PE virus,Win32 Foroux
    2,No significant change.No bug fixed.No any payload.
    About Win32 Foroux (plz keep the name,thanx)
    1,Full compatible Win32 PE virus on Win9X/2K/NT/XP'
    2,With very interesting feature.Check it!
    3,No any payload.No any optimization'
    4,Not bug free,because of a hurry work.No more than three weeks
    from having such idea to accomplishing coding and testing'
  • The worm drops an Elkern variant. Unlike the previous Klez versions, Klez.H puts the virus dropper into \Program Files\ folder with a random name and activates it.
  • The worm added 2 more names to the list of anti-virus companies that it previously had. These new names are:
    • Trendmicro
    • Kaspersky
    These names are used by the worm to compose messages when it sends itself as a virus removal tool from anti-virus companies.
  • The latest Klez variants, including Klez.H, can send out user's files with its message. The worm can randomly pick a file with one of the following extensions and attach it to its infected message:
    • .txt
    • .htm
    • .html
    • .wab
    • .asp
    • .doc
    • .rtf
    • .xls
    • .jpg
    • .cpp
    • .c
    • .pas
    • .mpg
    • .mpeg
    • .bak
    • .mp3
    • .pdf
    So in some cases, the user's confidential data can be sent out from an infected system.





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