This indicates the presence of a growingly popular peer-to-peer (P2P) Voice-over-IP (VoIP) application, known as Skype, in your network.

Skype is a P2P application designed specifically to provide high-quality Internet telephony. It uses a proprietary protocol to set up and manage all VoIP calls, along with instant messaging. This may cause two problems from an organization viewpoint. One is the excessive consumption of network bandwidth. The other is possibly undetected virus transmission, since all Skype traffic is encrypted by default.