Using a 10 years old security gap you can be identified by any webmaster. Don’t believe it?
If you are a member of Xing, facebook, StudiVZ or of any other social networking plattform, just go and give it a try: http://126.96.36.199/experiment/nwcheck.php
In their 15 page paper the four students Thorsten Holz, Gilbert Wondracek, Engin Kirda und Christopher Kruegel describe how every social network user can be identified by his unique digital fingerprint. What makes every user uniquwe is the consistency of group membership and usage in his or her favourite network – be it Xing, facebook or any other. This allows to clearly identify every single user, given he is a member in one of the social communities and given that he makes use of groups. The security hole lies in browser history which is being archived and fairly easy to access.
If you are interested in the complete details of how it works and what you can do to reduce the risk, simply download their paper: http://www.iseclab.org/papers/sonda-TR.pdf (803 kb).