Report: NSA agents spying on virtual worlds of 'World of Warcraft,' 'Second Life'

(CNN) - Government spies have been infiltrating the virtual worlds of online video games like 'World of Warcraft' and 'Second Life,' trying to recruit informants and stop terror attacks before they happen, according to a joint investigation by The New York Times, Pro Publica, and The Guardian, based on documents leaked by former National Security Agency contractor Edward Snowden.

The Guardian's U.S. national security editor Spencer Ackerman called it "a horde of undercover orcs."

But how a militant or terrorist group might use such a game to launch an attack is unclear, he says.

"The suspicion around the sort of late 2000s that emerged in intelligence circles, in defense circles, was that as more of our lives migrate into massively multiple online role-playing games like Warcraft and others, more people would seek to use them as sort of online sanctuaries, where you wouldn't think intelligence agencies like the NSA would be watching," said Ackerman.

It remains unclear how many agents might be playing such online games at any one time. CNN has not received an on-the-record response to these reports from the NSA, but the agency does say its programs are all centered on valid foreign intelligence targets.

"They collected quite a lot of data," said Ackerman. "It wasn't targeted to particular individuals, but was an 'opportunity' – as one of the documents describes the online role-playing world."

Asked if any terrorists have actually been caught by entering these online worlds, Ackerman said, "Not to my knowledge."

"There has been a great deal of effort not just by the NSA, but by the U.S. Central Command, to try and put people pretending to be either gamers, or people in chat rooms otherwise seemingly unaffiliated with these groups, to try and penetrate these networks," said Ackerman.

But there appears to be little to suggest that online environments led to actual terrorist plots, and not much evidence of how much useful intelligence was collected out of them, said Ackerman.

CNN's Edward Meagher contributed to this report.