Most antivirus products are not very good at finding Trojans, unfortunately.
A product that may eliminate this problem on your machine is PestPatrol, from www.pestpatrol.com. Another option is The Cleaner, from www.moosoft.com.
For more information on this topic, visit these other SearchSecurity resources:
Best Web Links: Malware
Ask the Expert: A Trojan horse on a home computer
This was first published in June 2002