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Welchi.B

Classification

Category: Malware

Type: Worm

Aliases: Welchi.B, Nachi.B, Welchia.B

Summary


A new variant of the Welchi RPC worm was found on February 12th, 2004.

This variant is functionally quite similar to the original virus. It copies itself on the infected system as SVCHOST.EXE.

The worm contains links to several security patches and will try to install them. Welchi.B will also try to remove Mydoom.

It might display a text saying "LET HISTORY TELL FUTURE !" and references to the dropping of atomic bombs during seconds world war.

Removal


Automatic action

Based on the settings of your F-Secure security product, it will either automatically delete, quarantine or rename the detected program or file, or ask you for a desired action.

Knowledge Base

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About the product

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Submit a sample

Submit a file or URL for further analysis.

Technical Details


The worm will start by creating a mutex named "WksPatch_Mutex" after which it will install itself as a service.

It copies itself to the Windows' System folder as "svchost.exe"

Whenever the system's date is within the month of June it will remove itself.

On certain occasions the worm attempts to download one of the following Windows patches:

  • https://download.microsoft.com/download/4/d/3/4d375d48-04c7-411f-959b-3467c5ef1e9a/WindowsXP-KB828035-x86-CHS.exe
  • https://download.microsoft.com/download/a/4/3/a43ea017-9abd-4d28-a736-2c17dd4d7e59/WindowsXP-KB828035-x86-KOR.exe
  • https://download.microsoft.com/download/e/a/e/eaea4109-0870-4dd3-88e0-a34035dc181a/WindowsXP-KB828035-x86-ENU.exe
  • https://download.microsoft.com/download/9/c/5/9c579720-63e9-478a-bdcb-70087ccad56c/Windows2000-KB828749-x86-CHS.exe
  • https://download.microsoft.com/download/0/8/4/084be8b7-e000-4847-979c-c26de0929513/Windows2000-KB828749-x86-KOR.exe
  • https://download.microsoft.com/download/3/c/6/3c6d56ff-ff8e-4322-84cb-3bf9a915e6d9/Windows2000-KB828749-x86-ENU.exe

It will scan the computer for files with extensions from the following list:

.shtml
.shtm
.stm
.cgi
.php
.html
.htm
.asp
 

And overwrite them with and HTML contained within the worm's body, the exact HTML code follows:

LET HISTORY TELL FUTURE !

 1931.9.18

1937.7.7

1937.12.13 300,000 !

 1941.12.7

1945.8.6 Little boy

1945.8.9 Fatso

 1945.8.15

Let history tell future !

Access to the Internet will be checked by attempting to resolve randomly any of:

microsoft.com
intel.com
google.com
 

In case of failure, it will wait for 20 minutes before attempting the operation again.

Spreading.

The worm will spread through the backdoor left in the system by the Mydoom.A and Mydoom.B worms.

In addition it will use the same exploits as the original Welchi variant, information about those can be found from the Welchi description:

https://www.f-secure.com/v-descs/welchi.shtml