BOAC,
I'm not sure if there would be a file that can easilt be checked. If you could find one, you could probably remove any hidden programs controlling the machine. The best thing to do would be to run an up-to-date anti-virus program, and then either
Spybot or
AdAware. Spybot looks to be a little more thorough and can immunize your computer against some malicious programs. After that, strongly encourage your users to set up ZoneAlarm. ZoneAlarm can track where outbound connections are going.
goates