How Unique and Traceable Are Usernames?
Usernames are ubiquitously used for identification and authentication purposes on web services and the Internet at large, ranging from the local-part of email addresses to identifiers in social networks. Usernames are generally alphanumerical strings chosen by the users and, by design, are unique within the scope of a single organization or web service. In this paper, the authors investigate the feasibility of using usernames to trace or link multiple pro les across services that belong to the same individual. The intuition is that the probability that two usernames refer to the same physical person strongly depends on the "Entropy" of the username string itself.