Scientists find way to stalk via Skype

Users of videoconferencing software Skype are at risk of being stalked online, after scientists found a low-cost way to track them via their Internet Protocol (IP) addresses. According to UK’s The Register, the method traces the Skype users’ online activities such as the sharing of specific files over peer-to-peer networks like BitTorrent. “We have shown that it is possible for an attacker, with modest resources, to determine the current IP address of identified and targeted Skype user[s] (if the user is currently active)," the Register quoted the scientists as saying in a 14-page paper. The method works even when Skype users configure their accounts to accept calls only from those in their contact lists, the report said. Scientists also said the method works against Skype users who are not currently logged in, but had used the program in the past three days, it added. The system can even link an individual Skype user to specific BitTorrent activity even when they share the IP address with others over a local area network that uses network address translation. “In the case of Skype, even if the targeted user is behind a NAT, the attacker can determine the user's public IP address. Such an attack could be used for many malicious purposes, including observing a person's mobility or linking the identity of a person to his internet usage," the paper said. Worse, the scientists found that it was relatively easy to find the ID of most Skype users when their email address and birth name are known to the attacker. Additional information, such as the target's city of residence, sex, or age, brought greater accuracy to the task. The scientists called the target's Skype account using a customized system that sent specially crafted packets. By examining the headers of the data that was returned, they can determine the person's IP address. Because the scientists prevented a TCP, or transmission control protocol, connection from being fully established during the probing, targets had no idea their Skype accounts were being tracked. The scientists devised the system so that it could track 10,000 people for about $500 per week. After learning the IP addresses of individuals, the scientists tapped BitTorrent sites to track the specific downloads of addresses in their database. Even when one of the IP addresses was shared among many users on a single network, the method was able to single link a unique Skype user to a specific download by, among other things, collecting identifiers known as info-hashes from BitTorrent networks. The scientists said similar real-time communications applications like Google Talk, MSN Live [were also found to] be susceptible to the technique, but they singled Skype out for containing what they called “a major privacy vulnerability." Security upgrade Adrian Asher, chief information security officer in Microsoft's Skype division, said they are committed to making their products as secure as possible. “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," he said. The research paper titled “I Know Where You are and What You are Sharing" made several recommendations for improving Skype's ability to conceal the identity of its users. “One solution that would go a long way is to design the VoIP system so that the callee's IP address is not revealed until the user accepts the call," it said. Such a property will not allow a person to inconspicuously call another. Moreover, if the caller is not on the contact list, and the one being called configured his or her software not to accept calls from anyone outside his contact list, “then this design would prevent any stranger from tracking him, conspicuously or otherwise." — LBG, GMA News