Marc001
Just an additional suggestion that other members may or may not like:
Do you have a firewall?
A firewall will protect you from random and malicious connections as well as anything someone may try to download to your PC, like a worm or Trojan.
I note that this is not really what you are complaining about but it is better to be safe than sorry.
PeerGuardian 2.0
This freebie software is similar to a mini firewall but, unlike a firewall, it protects your PC on the IP level. It stops various IPs (companies) getting into your PC via port 6346 and, the part you could be interested in, you can specify a range of IP addresses, by putting in the first and last IP address, you want to keep out of your PC.
So all in all, PeerGuardian 2.0 seems to be the software for you, available from here:
http://www.methlabs.org
UK Bob