Criminals beware! US law enforcement authorities may be stalking you on Facebook, MySpace, LinkedIn or Twitter.
Justice Department and Internal Revenue Service (IRS) documents obtained by the Electronic Frontier Foundation (EFF) reveal some of the ways the FBI and tax agents are allowed to use social networks for investigative purposes.
The documents were posted last week on the website of the EFF after being obtained through a lawsuit filed under the Freedom of Information Act by the San Francisco-based electronic rights group and the Samuelson Clinic of the University of California, Berkeley.
The key documents are from a 2009 training course for IRS employees and an August 2009 Justice Department presentation on Obtaining And Using Evidence From Social Networking Sites."
The IRS document clearly states that employees are not allowed to use false identities to scour social networking accounts while conducting a probe into a taxpayer.
"Generally, you are allowed to review information from publicly accessible, unrestricted websites," the document says.
"Employees may not use either their correct identification information or false identification information to become 'friends' to gain access to the taxpayer's social network site."
The Justice Department presentation on the other hand includes a slide on "undercover operations" and asks "Why go undercover on Facebook, MySpace etc?"
Among the reasons cited may be to "communicate with suspects/targets," to "gain access to non-public info" or to "map social relationships/networks," it says.
The presentation also asks "if agents violate terms of service, is that 'otherwise illegal activity.'"
The terms of use of most social networks bar the use of fake identities or impersonation. The Justice Department document lists a number of ways in which evidence from social networking sites can be useful including to "reveal personal communications" or "establish motives and personal relationships."
Social networks can also be used to "provide location information," to "prove and disprove alibis" or to "establish crime or criminal enterprise."
The Justice Department said Facebook is "often cooperative with emergency requests" while Twitter has a "stated policy of producing data only in response to legal process."
MySpace "requires a search warrant for private messages/bulletins less than 181 days old," the Justice Department said, while LinkedIn's "use for criminal communications appears limited."
Andrew Noyes, a Facebook spokesman, outlined the company's policies in an email to AFP.
"Like other companies holding personal records - from phone records to medical history - Facebook works with law enforcement to the extent required by law and where appropriate to ensure the safety of Facebook users," he said.
"Our goal is to respect the balance between law enforcement's need for information and the privacy rights of our users, and as a responsible company we adhere to the letter of the law," Mr Noyes said.
"We scrutinise every single law enforcement request; require a detailed description of why the request is being made; and if it is deemed appropriate, share only the minimum amount of information," he said.
Regarding emergency requests, Mr Noyes said "in rare instances our policies and the law allow for emergency sharing.
"One hypothetical is the case of a kidnapped child where every minute counts. In instances like this, where we've verified an emergency, we feel a responsibility to quickly share information that could save someone's life."
Christopher Wolf, co-chair of the Future of Privacy Forum, said the documents raise a "number of questions" but "by no means indicate that the government or social media have crossed the line."
"Web users, users of social networks should be cautious of everything they post online, regardless of law enforcement action," Mr Wolf said.