Pinterest has removed its "warrant canary" from its terms and conditions, indicating it may have been served with a subpoena by the FBI.
The term "warrant canary" refers to an item in a service provider's transparency report or other regularly published statement that says how many subpoenas or warrants it has been issued with for information it holds on users.
These canaries usually refer directly to a National Security Letter, a subpoena for the seizure of information for national security purposes that the FBI can issue directly without going through a judge.
Typically, these letters also carry a non-disclosure order, meaning the subject cannot directly report that such a letter has been received. There is one caveat, however, in that the recipient of the warrant is allowed to report the number of these letters it receives in batches of 250 every six months.
In the case of Pinterest, the image-sharing site had been issuing a transparency report every quarter since 2013 containing a warrant canary that had, until now, simply read "National security: 0".
In its 2015 report, however, this now reads "0-249", indicating the company has potentially received at least one National Security Letter from the FBI in that time.
Digital rights campaign group the Electronic Frontier Foundation, which has been championing "Canary Watch" - an initiative to note when warrant canaries seem to die - said the increase from 0 to 249 "is certainly the strong implication that Pinterest did receive a national security request, because it would have otherwise have continued to report 0".
However, the organisation also added a note of caution, saying: "in our time working with Canary Watch we have seen many canaries go away and come back, fail to be updated, or disappear altogether along with the website that was hosting it.
"Until the gag orders accompanying national security requests are struck down as unconstitutional, there is no way to know for certain whether a canary change is a true indicator. Instead, the reader is forced to rely on speculation and circumstantial evidence to decide what the meaning of a missing or changed canary is."
