Tens of thousands of pirate gamers have been enslaved in a Bitcoin botnet after downloading a cracked copy of popular game Watch Dogs.

A torrent of the infected title, which supposedly has had its copy-protection removed, had almost 40,000 active users (seeders and leechers) and was downloaded a further 18,440 times on 23 May on one site alone.

Pirates reported on internet forums that the torrent package masquerading under the popular torrent brand SkidRow had quietly installed a Bitcoin miner along with a working copy of the game.

The Windows miner ran via two executables installed in the folder AppData\Roaming\OaPja and would noticeably slow down lower performance machines sucking up to a quarter of CPU power.

Most sources have removed the offending torrent. Analysis has yet to be done to determine the location or identities of actors behind the attack.

Gamers were choice targets for Bitcoin mining malefactors because they often ran high-end graphical processing units (GPUs) and shunned resource-draining anti-virus platforms.

"If you happen to download cracked games via Torrent or other P2P sharing services, chances are that you may become a victim of [a] lucrative trojan bundled with a genuine GPU miner," BitDefender chief strategist Catalin Cosoi said of an early Bitcoin miner that targeted gamers.

"We advise you to start checking your system for signs of infection, especially if you are constantly losing frames-per-second."

Using stolen dispersed compute resources was one of the few ways punters could make decent cash by crunching the increasingly difficult mathematical algorithms required to earn Bitcoins.

Crims have in recent years foisted the compute-intensive Bitcoin miners in a host of attacks targeting valuable high-end GPUs right down to ludicrously slow digital video recorders. ®