Is Skype Really a Threat?
Skype is a peer-to-peer (P2P) application, meaning that users connect to one another directly and not through a central server for communication. Skype initially uses Internet-based servers to authenticate users when they log in and to track their status, but when a “chat” or instant message, “voice call” or “file transfer” is initiated, the parties involved in the communication do so in a P2P direct connection. If one or both of the users are behind a typical corporate Network Address Translation (NAT) firewall, the communication can be relayed through a Supernode because a direct P2P can’t be established behind a NAT. In the case of a file transfer, you will see a message indicating your transfer is being relayed.
One of security professionals’ primary concerns about Skype are it’s so easy for a Skype client to find a way around a secure corporate firewall configuration. Skype does this by using ports 80 and 443, which are open in most firewalls to allow Web browsing. In addition, Skype may reroute traffic if the initial port assigned during the Skype installation isn’t available. This makes blocking Skype at a firewall more difficult since the ports Skype uses can change as needed.
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