Hi Keef
The problem might not be on your PC. Have you changed anything on your router? Skype is a peer to peer application. Your PC resources are used to route other peoples calls in a "swarm", similar to torrent applications. In fact, it was developed from Kazaa.
You may have unwittingly become a Skype "supernode" but, in theory, only if your firewall is turned off.
| Computerworld NZ
It's possible to configure your router to stop this and there is a setting in Skype itself (or perhaps it was a registry key) to turn off the peer-peer routing aspect. Google will assist.
Note that when you accepted the Skype license agreement, you consented to Skype using your resources.
Cheers