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Pseudonymity is a word derived from pseudonym, meaning 'false name', and anonymity, meaning unknown or undeclared source, describing a state of mistaken disguised identity. The pseudonym identifies a holder, that is, one or more human beings who possess but do not disclose their true names (that is, legal identities).[1] Most pseudonym holders use pseudonyms because they wish to remain anonymous, but anonymity is difficult to achieve, and is often fraught with legal issues.[2] True anonymity requires unlinkability, such that an attacker's examination of the pseudonym holder's message provides no new information about the holder's true name.[3]



Although the term is most frequently used today with regard to identity and the Internet, the concept of pseudonymity has a long history. For example, all of the Federalist Papers were signed by Publius, a pseudonym representing the trio of James Madison, Alexander Hamilton, and John Jay. The papers were written partially in response to several Anti-Federalist Papers, also written under pseudonyms. As a result of this pseudonymity, historians know that the papers were written by Madison, Hamilton, and Jay, but have not been able to discern which of the three authored certain papers.

Pseudonymity has become an important phenomenon on the Internet and other computer networks. In computer networks, pseudonyms possess varying degrees of anonymity,[4] ranging from highly linkable public pseudonyms (the link between the pseudonym and a human being is publicly known or easy to discover), potentially linkable non-public pseudonyms (the link is known to system operators but is not publicly disclosed), and unlinkable pseudonyms (the link is not known to system operators and cannot be determined).[5] For example, true anonymous remailer enables Internet users to establish unlinkable pseudonyms; those that employ non-public pseudonyms (such as the now-defunct Penet remailer) are called pseudonymous remailers.

The continuum of unlinkability can also be seen, in part, on Wikipedia. Some registered users make no attempt to disguise their real identities (for example, by placing their real name on their user page). The pseudonym of unregistered users is their IP address, which can, in many cases, easily be linked to them. Other registered users prefer to remain anonymous, and do not disclose identifying information. However, Wikipedia's server logs may enable system administrators to determine the IP address, and perhaps the true name, of a registered user (see Wikipedia:Privacy Policy for a list of the conditions under which such a linkage would be attempted). It is possible, in theory, to create an unlinkable Wikipedia pseudonym by using an Open proxy, a Web server that disguises the user's IP address. However, most open proxy addresses are blocked indefinitely due to the their frequent use by vandals (see Wikipedia:Blocking policy). Additionally, Wikipedia's public record of a user's interest areas, writing style, and argumentative positions may still establish an identifiable pattern.[6] [7]

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