It's been more than a year since the WSJ reported that Skype leaks its users' IP addresses and locations. Microsoft has done nothing to fix this since, and as Brian Krebs reports, the past year has seen the rise of several tools that let you figure out someone's IP address by searching for him on Skype, then automate launching denial-of-service attacks on that person's home.
In the above screen shot, we can see one such service being used to display the IP address most recently used by the Skype account "mailen_support" (this particular account belongs to the tech support contact for Mailien, a Russian pharmacy spam affiliate program by the same name).
Typically, these Skype resolvers are offered in tandem with "booter" or "stresser" services, online attack tools-for-hire than can be rented to launch denial-of-service attacks (one of these services was used in an attack on this Web site, and on that of Ars Technica last week). The idea being that if you want to knock someone offline but you don't know their Internet address, you can simply search on Skype to see if they have an account. The resolvers work regardless of any privacy settings the target user may have selected within the Skype program's configuration panel.
Beyond exposing one's Internet connection to annoying and disruptive attacks, this vulnerability could allow stalkers or corporate rivals to track the movement of individuals and executives as they travel between cities and states.