Not limiting their activities to the earthly realm, US and British spies have infiltrated the fantasy worlds of World of Warcraft and Second Life, conducting surveillance and scooping up data in the online games played by millions of people across the globe, according to newly disclosed classified documents.

Fearing that terrorist or criminal networks could use the games to communicate secretly, move money or plot attacks, the documents show, intelligence operatives have entered terrain populated by digital avatars that include elves, gnomes and supermodels.

Spot the spook: intelligence operatives have entered the terrain populated by digital avatars that include elves, gnomes and supermodels - such as these from online game Second Life.

The spies have created make-believe characters to snoop and to try to recruit informers, while also collecting data and contents of communications between players, according to the documents, disclosed by the former National Security Agency contractor Edward J. Snowden. Because militants often rely on features common to video games - fake identities, voice and text chats, a way to conduct financial transactions - US and British intelligence agencies worried that they might be operating there, according to the papers.

Online games might seem innocuous, a top-secret 2008 NSA document warned, but they had the potential to be a "target-rich communication network" allowing intelligence suspects "a way to hide in plain sight." Virtual games "are an opportunity!" another 2008 NSA document declared.