A 'warrant canary' in the annual transparency report of the social news site Reddit has been removed, sparking fears it has received a secret government order to hand over user data.

A warrant canary is a system used by websites to indirectly inform its users that it has been issued with a secret order for information.

Since these orders cannot legally be spoken about by the recipients, a 'warrant canary' can be used to specify one has not been received. If the canary disappears, it suggests one has been.

Reddit, a site where users can post, vote and comment on new stories, videos and pictures, publishes a report every year which lists all the government requests for user information made in the previous 12 months.

A canary was present in 2014's report, in a paragraph which specified the site had "never received a National Security Letter, an order under the Foreign Intelligence Surveillance Act, or any other classified request for user information."

There is no similar paragraph in the most recent report, suggesting Reddit could have received a secret order to hand over user data at some point in 2015.

Obviously, Reddit was not able to confirm nor deny whether it had received such an order.

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Steve Huffman, co-founder and CEO of the website, said: "I've been advised not to say anything one way or the other," when asked about the canary's absence, a statement which some users saw as a veiled admission that an order had been made.

The FBI can use national security letters to force internet and telecoms companies to hand over user data, including web browsing history and records of online purchases.

Users can create a Reddit account without handing over any personal information, meaning the government would gain little if they did issue a secret order to the company.

However, users' IP addresses, the numbers which correspond to specific computers, could theoretically be used to identify them, as could the details of their private messages.

According to the report, Reddit received 98 requests for user data in 2015. It handed over in 60 per cent of cases, affecting 142 users in total.

53 requests for the removal or blocking of content were made in the same year, 21 per cent of which were agreed to.