NEW YORK, USA: U.S. law-enforcement agencies are increasingly obtaining warrants to search Facebook, often gaining detailed access to users' accounts without their knowledge.

A Reuters review of the Westlaw legal database shows that since 2008, federal judges have authorized at least two dozen warrants to search individuals' Facebook accounts. Many of the warrants requested a laundry list of personal data such as messages, status updates, links to videos and photographs, calendars of future and past events, "Wall postings" and "rejected Friend requests."

Federal agencies include FBI, DEA and ICE

Federal agencies seeking the warrants include the FBI, DEA and ICE, and the investigations range from arson to rape to terrorism.

The Facebook search warrants typically demand a user's "Neoprint" and "Photoprint" -terms that Facebook has used to describe a detailed package of profile and photo information that is not even available to users themselves.

These terms appear in manuals for law enforcement agencies on how to request data from Facebook. The manuals, posted on various public-advocacy websites, appear to have been prepared by Facebook, although a spokesman for the company declined to confirm their authenticity.

The review of Westlaw data indicates that federal agencies were granted at least 11 warrants to search Facebook since the beginning of 2011, nearly double the number for all of 2010. The precise number of warrants served on Facebook is hard to determine, in part because some records are sealed, and warrant applications often involve unusual case names. (One example: "USA v. Facebook USER ID Associated with email address jimmie_white_trash@yahoo.com," a sealed case involving a drug sale.)

In a telephone interview, Facebook's Chief Security Officer, Joe Sullivan, declined to say how many warrants had been served on the company. He said Facebook is sensitive to user privacy and that it regularly pushes back against law-enforcement "fishing expeditions."

Not challenged

None of the warrants discovered in the review have been challenged on the grounds that it violated a person's Fourth Amendment protection against unlawful search and seizure, according to a review of the cases.

Some constitutional-law experts said the Facebook searches may not have been challenged because the defendants - not to mention their "friends" or others whose pages might have been viewed as part of an investigation -- never knew about them.

By law, neither Facebook nor the government is obliged to inform a user when an account is subject to a search by law enforcement, though prosecutors are required to disclose material evidence to a defendant.

Twitter and several other social-media sites have formally adopted a policy to notify users when law enforcement asks to search their profile.

Last January, Twitter also successfully challenged a gag order imposed by a federal judge in Virginia that forbade the company from informing users that the government had demanded their data.

Twitter said in an email message that its policy was "to help users protect their rights." The Facebook spokesperson would not say whether the company had a similar policy to notify users or if it was considering adopting one.