Usernames are ubiquitous on the Internet. Almost every web site uses them to identify its users and, by design, they are unique within each service. In web services that have millions or hundreds of millions of users, it might become difficult to find a username that has not already been taken. For instance, you might have experienced that a specific username you wanted was already taken. This phenomenon drives users to choose increasingly complex and unique usernames.
Our experiments show that most usernames constitute extremely identifying pieces of information. We built a tool to estimate how unique and linkable usernames are and made it available on this page for you to check. For example, according to our tool, “ladygaga” or “12345678″ only carry 24 and 17 bits of entropy, respectively. They are therefore not likely to be unique on the Internet. On the other hand, usernames such as “pdjkwerl” or “yourejerky” carry about 40 bits of entropy and are therefore very good identifiers.
Type your username (for example “zorro1982″ or “dan.perito”) to discover how unique it is. This tool can help you to select an username that has low entropy and can’t be used to track you on the Internet.
Alternatively, try typing two usernames separated by a space. The tool will give an estimation on whether the two usernames are linkable.
How unique and traceable are usernames? Privacy Enhancing Technologies Symposium, PETS 2011 [PDF]