The annual Def Con hacking convention has asked the US federal government to stay away this year for the first time in its 21-year history, saying Edward Snowden's revelations have made some in the community uncomfortable about its presence.

It would be best for everyone involved if the Feds call a 'time-out' and not attend Def Con this year," conference founder Jeff Moss said in an announcement posted Wednesday night on the convention's website.

A crowd of more than 15,000 hackers, researchers, corporate security experts, privacy advocates, artists and others are expected to attend the Las Vegas convention, which begins on August 2.

The conference has attracted officials from agencies, including the Central Intelligence Agency, National Security Agency, Federal Bureau of Investigations, Secret Service and all branches of the military.

The government had previously always been welcome at Def Con, where hackers have held tongue-in-cheek "spot the Fed" contests to identify government officials in the crowd.