Summary

Fourcourse is a Visual Basic Script trojan which consists of two VBS files. The first file carries another Visual Basic Script which it drops in the root of C: drive as sysw32.vbs.

It also changes Windows registry by adding the following key:

HKLM\Software\Microsoft\Windows\CurrentVersion\Run\sysw32= C:\sysw32.vbs

So the next time the system is restarted, the trojan in sysw32.vbs is executed. If the system date is after April 1st, 2003 the script code in sysw32.vbs tries to use all four COM ports to dial a phone number.

F-Secure Anti-Virus detects Fourcourse trojan with the updates published on March 11th, 2003:

[FSAV_Database_Version]
Version=2003-03-11_03

[Analysis: Katrin Tocheva and Sami Rautiainen; F-Secure Corp.; March 11th, 2003]