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