We are all aware that our online lives, including our accounts on social networks, aren't always private and safe. But other than the threat of hackers, the government may also be spying on us using our online accounts, as exemplified by Twitter.

The social media platform announced Friday it received two national security requests, one each in 2015 and 2016, asking for users' account data without informing the affected users. The company could not reveal this earlier since it was bound by gag orders until now that restricted it from openly speaking about the matter.

The requests were received in the form of national security letters (NSLs).

“We have provided each of the account holders with copies of the relevant NSLs (certain information redacted to protect privacy) as well as the account data we were compelled to produce,” the company said in an official blog post.

The letters have also been published on Twitter’s blog. The revelation follows similar admissions from Google and Yahoo in recent months.

Each letter requests a special kind of data called electronic communication transaction records, including email header data and browsing history.

FBI requests go far beyond the limitations set by a 2008 Justice Department legal memo, which said such orders could only be restricted to phone billing records.

“While the actual NSLs request a large amount of data, Twitter provides a very limited set of data in response to NSLs consistent with federal law and interpretive guidance from the U.S. Department of Justice,” the company’s blog post added.

NSLs are government orders used for obtaining communication data available to service providers. They are usually accompanied by a gag order restricting the provider from informing the user whose data is obtained. The legal tool has been available since the 1970s, but has been put into regular usage for varied purposes since the passing of the U.S.A. Patriot Act, passed shortly after Sept. 11, 2001, terror attacks.

The use of NSLs to obtain data is being opposed by major tech companies including Twitter which is fighting its own lawsuit against the government — Twitter v. Lynch.