Welchi.B

Classification

Malware

Worm

W32

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 move the file to the quarantine where it cannot spread or cause harm, or remove it.

Suspect a file is incorrectly detected (a False Positive)?

A False Positive is when a file is incorrectly detected as harmful, usually because its code or behavior resembles known harmful programs. A False Positive will usually be fixed in a subsequent database update without any action needed on your part. If you wish, you may also:

  • Check for the latest database updates

    First check if your F-Secure security program is using the latest detection database updates, then try scanning the file again.

  • Submit a sample

    After checking, if you still believe the file is incorrectly detected, you can submit a sample of it for re-analysis.

    NOTE If the file was moved to quarantine, you need to collect the file from quarantine before you can submit it.

  • Exclude a file from further scanning

    If you are certain that the file is safe and want to continue using it, you can exclude it from further scanning by the F-Secure security product.

    Note You need administrative rights to change the settings.

Find out more

Knowledge Base

Find the latest advice in our Community Knowledge Base.

User Guide

See the user guide for your product on the Help Center.

Contact Support

Chat with or call an expert for help.

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