A Skype vulnerability which can expose the location, identity and the content a user is downloading has been discovered by researchers.Spokespeople for Microsoft, which owns Skype, said that engineers are working on the problem.

The issue was uncovered earlier this year by a team of researchers from Polytechnic Institute of New York University (NYU-Poly), MPI-SWS in Germany and INRIA in France and included Keith Ross, Stevens Le Blond, Chao Zhang, Arnaud Legout and Walid Dabbous. The team presented the research in Berlin recently at the Internet Measurement Conference 2011 in a paper titled "I know where you are and what you are sharing."

The researchers found several properties of Skype that can track not only users' locations over time, but also their peer-to-peer (P2P) filesharing activity, according to a summary of the findings. Earlier this year, a German researcher found a cross-site scripting flaw in Skype that could allow someone to change an account password without the user' consent.

"Even when a user blocks callers or connects from behind a Network Address Translation (NAT), a common type of firewall, it does not prevent the privacy risk," according to a statement from NYU-Poly.

The research team tracked the Skype accounts of about 20 volunteers as well as 10,000 random users over a two week period and found that callers using VoIP systems can obtain the IP address of another user when establishing a call with that person. The caller can then use commercial geo-IP mapping services to determine the other user's location and internet Service Provider (ISP).

The user can also initiate a Skype call, block some packets and quickly terminate the call to obtain an unsuspecting person's IP address without alerting them with ringing or popup windows. Users do not need to be on a contact list, and it can be done even when a user explicitly configures Skype to block calls from non-contacts.

The research also revealed that marketers can easily link to information such as name, age, address, profession and employer from social media sites such as Facebook and LinkedIn in order to inexpensively build profiles on a single tracked target or a database of hundreds of thousands.

"We feel the implications are very severe," Ross said. "For example, a high school hacker or anyone with basic programming and hacking skills could track, for example, all the Congressmen in the United States, or the employees of a company. The attack can be used by blackmailers, stalkers or journalists looking for a racy story about a politician."

Skype and Microsoft were informed of the researchers' findings and The New York Times reported that Skype is aware of the issue. Spokespeople for Microsoft, which owns Skype, said that engineers are working on the problem.

"We value the privacy of our users and are committed to making our products as secure as possible," Adrian Asher, Skype's chief information security officer, said. "Just as with typical internet communications software, Skype users who are connected may be able to determine each other's IP address. Through research and development, we will continue to make advances in this area and improvements to our software."

Ross said until the issue has been addressed, he recommends that Skype account holders not leave their Skype application running and only have it on when in use. He also recommends screen names not be closely related to a person's actual name.