Microsoft has rolled out a new version of the desktop Skype client that should make users of its service a little safer from denial-of-service attacks. The Skype client has long leaked IP address information, allowing other users on the network to determine which IP address is being used by an account. A number of online services of various degrees of shadiness offer instant IP address lookups, and historically at least, these have worked effectively.
This leakage has been particularly widely abused in gaming communities. Many professional gamers last year were disrupted by denial-of-service attacks. Players were forcibly disconnected from the game, causing their team to play at a disadvantage. Skype, which is often used for coordinating games and in-team communication, was routinely fingered as the culprit since it leaks the IP address information of the players and thus enables these attacks.
The information leakage is likely a relic of Skype’s peer-to-peer nature; the IP address of each user had to be disseminated in order to enable direct peer-to-peer connections to those users. But for some time, the client has had an option to hide your IP address from people who aren’t on your contact list. In this mode, any traffic between non-contacts goes through Microsoft’s servers, and IP addresses aren’t readily disclosed. Judicious use of this option protects your address from the various IP address lookup services, thereby protecting against denial of service attacks.
Skype will enable the new feature by default
That option is now on by default, making accidental information leakage much less likely. With this option, people on your contacts list will still in principle be able to figure out your IP.