Try this out. Open a command window and type in "netstat -abno". You'll get a list of active network ports on your machine and what programs are using them. You'll see the connection type (TCP/UDP), the Local IP Address:port number connected to/in use, the Foreign IP Address:port number in use, the state of the connection (active, listening, established, waiting), the PID (Process ID), and the name of the executable responsible for this activity.
This can be a useful tool when configuring firewalls and when investigating actively sniffing viruses.
-- Matt Ranlett
PS - more about netstat
here and
here