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Gokar


Aliases:


Gokar
W32/Gokar@mm, Karen

Malware
Worm
W32

Summary

Gokar is a combination of e-mail, IRC and IIS web worm. It was found in the wild early on December 13th, 2001.Gokar sends itself via Microsoft Outlook, using a long list of variable subject fields, contents and attachment names. The attachment always has an extension of PIF, SCR, COM, EXE or BAT.

An infected machine can be manually detected by checking the existance of KAREN.EXE in Windows directory.

If the infected machine is working as a web server, the worm will modify the Microsoft IIS starting page to offer WEB.EXE to be downloaded by all visitors to the website.

Gokar also modifies mIRC chat client configuration to spread to worm further via IRC chats.

Gokar is detected by F-Secure Anti-Virus update shipped on 13th of December.



Disinfection & Removal

Automatic Disinfection

Allow F-Secure Anti-Virus to disinfect the relevant files.

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



Technical Details

The worm is written in Visual Basic and has been compressed by the UPX file compressor.

The worm infects a computer when a user opens an infected attachment. The worm copies itself as KAREN.EXE into Windows folder and modifies Registry to be always run with Windows. The worm's file has hidden attribute. Then the worm creates the following key:

[HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run]
 "Karen" = "<windir>\karen.exe"

Where &lt;windir&gt; is Windows directory name.

After that the worm opens Outlook Address book and sends itself to all e-mail addresses it can find there. The infected messages can have different subjects and bodies:

Subject can be one of the following:

If I were God and didn't belive in myself would it be blasphemy
 The A-Team VS KnightRider ... who would win
 Just one kiss, will make it better. just one kiss, and we will be alright.
 I can't help this longing, comfort me.
 And I miss you most of all, my darling ...
 ... When autumn leaves start to fall
 It's dark in here, you can feel it all around. The underground.
 I will always be with you sometimes black sometimes white ...
 .. and there's no need to be scared, you re always on my mind.
 You just take a giant step, one step higher.
 The air will hold you if you try, trust my wings of desire. Glory, Glorified.......
 The horizons lean forward, offering us space to place new steps of change.
 I like this calm, moments before the storm
 Darling, when did you fall..when was it  over ?
 Will you meet me .... and we'll fly away ?!

Message bodies can contain one of the following:

You should like this, it could have been made for you
 speak to you later
 Hey
 They say love is blind ... well, the attachment probably proves it.
 Pretty good either way though, isn't it ?
 Happy Birthday
 Yeah ok, so it's not yours it's mine :)
 still cause for a celebration though, check out the details I attached
 This made me laugh
 Got some more stuff to tell you later but I can't stop right now
 so I'll email you later or give you a ring if thats ok ?!
 Speak to you later

After the body the worm puts Windows registered user name (the name of a person Windows is registered to).

The attachment name is randomly composed from a few parts that are hardcoded in the worm's body. The attachment can have .PIF, .SCR, .EXE, .BAT and .COM extension. Example:

r4354gkjwr4354gkjwr4354gkjw109897619073r4354gkjw.com

Here's an example of an infected message:

The worm also spreads via IRC. It replaces mIRC chat client's SCRIPT.INI file with its own one. This script allows the worm to send itself as KAREN.EXE to all people joining an IRC channel where an infected user is present. The worm sends itself with the following message:

If this doesn't make you smile, nothing will.

The worm looks for specific text messages in IRC channel and can change user's nickname to 'W32_Karen', 'W32Karen1', 'KarenWorm', 'KarenGobo' or join #teamvirus channel on certain messages.

The worm can also spread from a webpage. It checks if the infected machine has Microsoft IIS web server installed. It it is found the worm copies itself as WEB.EXE to root IIS folder, renames DEFAULT.HTM to REDESI.HTM (note: Redesi is the name of another virus) and creates its own DEFAULT.HTM page. If a visitor of a website opens this page, he will be asked to download WEB.EXE file. If a user accepts to 'Run this file from current location', the worm will be downloaded and activated on his system.

The worm looks for and terminates processes belonging to anti-virus and security software. The following processes are killed:

VSHWIN32.EXE  (McAfee)
  NAVAPW32.EXE  (Norton)
  _avpm.exe     (Kaspersky)
  avpm.exe      (Kaspersky)
  ICLOAD95.EXE  (Sophos)
  ICMON.EXE     (Sophos)
  IOMon98.exe   (Trend)
  VetTray.exe   (CA)
  Claw95.exe    (Norman)
  f-stopw.exe   (F-PROT)

Gokar is detected by F-Secure Anti-Virus update shipped on 13th of December.


Removal Instructions

To remove Gokar worm from your system please do the following:

1. Download and run the following REG file:

ftp://ftp.europe.f-secure.com/anti-virus/tools/gokardis.reg

2. Restart your system and scan your hard drive with F-Secure Anti-Virus (default settings). When FSAV detects Gokar infection in KAREN.EXE located in Windows directory, select 'Delete' disinfection action.

3. If Gokar worm infected a webserver, delete WEB.EXE file from C:\inetpub\wwwroot\ folder and rename REDESI.HTM (the original startup page renamed by the worm) back to DEFAULT.HTM. To do this open DOS session and type at command prompt (mind spaces):

c:
 cd  C:\inetpub\wwwroot
 del  web.exe
 ren  redesi.htm  default.htm

Press 'Enter' after each line.





Technical Details: F-Secure Anti-Virus Research Team; December 13th, 2001



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