A review by Reuters of federal search warrants in the Westlaw database shows that US law enforcement agencies received at least two dozen warrants (at least 11 since the beginning of 2011) to search Facebook accounts. In the Reuters article “A new U.S. Law-enforcement tool: Facebook searches," author Jeff John Roberts states that the warrant requests included information about messages, photos, status updates, calendars, wall postings and even rejected friend requests. The search warrants include terminology unique to Facebook, such as “Neoprint” and Photoprint.”
In one case, a psychiatrist who was under investigation by the DEA for running a “pill mill” had his Facebook records seized by search warrant. Statements that he made on Facebook and in “Mafia Wars,” a Facebook game, were used against him.
The Reuters article states that there is no requirement for Facebook to notify the user that an account has been searched. Facebook claims to notify users, but this might not always be the case.
The review by Reuters is only those warrants that are contained in the Westlaw database. Westlaw does not have that kind of information on state issued search warrants, and probably does not have every federal search warrant in their database either.
On one hand a lot of the information that people put on Facebook is not really protected by the Fourth Amendment right to be free from unreasonable searches, because the information is held by a third party. A person has no reasonable expectation of privacy about information that has been given to a third party who is an entity open to the public. Much of what a person puts on Facebook can be seen by friends on the site. It can be compared to things a person might yell in a crowded restaurant or bar.
On the other hand there is some information, such as messages between two people that are not available to other people on the site, even friends of the user. People do have an expectation of privacy in those situations. It is like having a private booth in a restaurant, with a curtain that is drawn to separate a more intimate conversation from the hearing of others.
The fact remains that information that a person posts online can and will be used against people in court. The recent Reuters article highlights a small slice of criminal law searches of Facebook accounts. Law enforcement and probation officers will gather information from Facebook posts that are available without a warrant, using just what a user makes available for the public. In the area of family law - custody, divorce, etc., the use of Facebook to see what another party has been doing and to gather evidence against them is very common.
Anyone who posts online has to ask themselves a few simple questions: Would I want this to be used against me or attributed to me in court? Am I talking about something or posting a picture about something that is against the law?