Summary

Smibag is a multi-component worm that attempts to send itself using a localized version (Korean) of MSN messenger. The worm is sent as SMB.EXE file. The worm drops adware components to an infected hard drive.

Additional Details

The SMB.EXE file that is send via MSN Messenger is a dropper. Inside it contains a ZIP archive and a decompression utility. When the dropper is run, it drops UZ.EXE and EXT.ZIP files and runs UZ.EXE utility to decompress the archive.

The archive contains the following files:

 admagic.exe - adware file
 atl.dll     - legitimate Windows component
 msnvc.exe   - file that sends the worm via MSN Messenger
 raw32x.dll  - data file
 sm.dll      - browser helper object file

The ADMAGIC.EXE file is then copied to the root of C: drive together with the dropper (SMB.EXE file). After that the UZ.EXE, ATL.DLL, RAW32X.DLL and SM.DLL files are copied to Windows System directory and the SM.DLL and ATL.DLL files are registered to Windows with Regsvr32.exe utility.

When the ADMAGIC.EXE adware file is run, it creates a startup key for itself in System Registry:

 [HKLM\Software\Microsoft\Windows\CurrentVersion\Run]
 "svchost" = "c:\admagic.exe"

This file is supposed to open Internet Explorer every 5 minutes. But we did not observe this behaviour on our test system. The file has a few adult website links in its body.

The worm attempts to spread using MSN Messenger as SMB.EXE file. The file that does the actual sending is MSNVC.EXE.

Detection

F-Secure Anti-Virus detects Smibag worm with the update released on October 1st, 2003:

[FSAV_Database_Version]
Version=2003-10-01_01

Technical Details: Alexey Podrezov

F-Secure Corporation; 1st of October, 2003