The number and variety of IP applications had a tremendous increase in the last few years. Besides, Internet applications of end users are changing with the wide spread of high performance PCs connected through the Internet using broadband links. In particular, the rapid increase in the number of users of Peer-to-Peer (P2P) network applications, due to the fact that users are easily able to use network resources over these overlay networks, also lead to a drastic increase in the overall Internet traffic volume. An accurate mapping of traffic to applications is important for a wide range of network management tasks, like traffic engineering, service differentiation, performance/failure monitoring, and security. However, traditional mapping approaches have become increasingly inaccurate because many applications use non-default or ephemeral port numbers, use well-known port numbers associated with other applications, change application signatures or use traffic encryption. This paper presents an approach, based on Principal Component Analysis, that is able to identify differentiating characteristics of different Internet applications, including several P2P file sharing protocols. The accuracy of the proposed approach was evaluated by performing a set of intensive tests and the results obtained show that it constitutes a valuable tool to identify peculiar characteristics of Internet applications while being, at the same time, immune to the most important disadvantages presented by other identification methods. Based on the achieved performance, we believe this methodology can form the basis for the development of an efficient application identification tool.