I keep getting a warning coming up on my PC from Norton Firewall telling me its blocked an attempt to hack my PC...

Security alert - High risk

Attempted to connect to local computer using the NetBus Trojan horse blocked...

This happens about once an hour, I've run both my anti virus programs and they haven't picked anything up, just about to run Spybot and see if that finds anything, but other than that I'm lost...

Anyone got any ideas?