Skype is an application that allows users to make voice calls over the Internet, using a proprietary VoIP network called the Skype protocol. After a user installs client software, calls to fellow Skype users are free-of-charge, while calls to landlines and mobile phones can be made for a fee. Additional features include instant messaging, file transfer and video conferencing. Skype is owned by Microsoft Corporation. Skype uses firewall evasion techniques and requires Encrypted Key Exchange signatures, in order to prevent or detect it.

This SonicWALL signature identifies one of several modes of network communications from Skype, but not all. In order to block Skype, you must all signatures in the application, as well as SIDs 5, and 7.