Microsoft released updates to its Skype Voice-over-IP (VoIP) application that included a privacy enhancement which enabled the default setting to hide users’ Internet Protocol (IP) addresses after researchers from Inria and Polytechnic Institute of New York University discovered they could track thousands of users for several weeks November 2010, which could have potentially led to attackers breaching business systems and stealing sensitive information, or compromising an entire – 6 – corporate network.
Source: http://www.securityweek.com/microsoft-finally-hides-ip-addresses-default-skype