If you've been playing Counter-Strike on the ESEA gaming network, you've been doing a lot more than tossing virtual hand grenades and firing virtual machine guns. You've been mining Bitcoins for an unnamed staffer inside the company that runs the network.

The mining started on April 13 and may have affected as many as 14,000 gamers.

ESEA distributes "anti-cheat" software that allows subscribers to play the Counter-Strike first-person shooter game on their network. The software gives players better data on their game play and cuts down on the use of known game cheats, which can give opponents an unfair advantage. The network has close to 14,000 paying customers, according to co-founder Craig Levine. He isn't sure how many customers had their machines used for mining, however.

Last month, ESEA started toying with the idea of adding a Bitcoin mining option to its anti-cheat client, but shelved the idea on April 12, Levine said in an e-mailed statement.

But the next day, an employee went ahead and started distributing the code "for his own personal gain," Levine says.

"What transpired the past two weeks is a case of an employee acting on his own and without authorization to access our community through our company’s resources. As of this morning, ESEA has made sure that all Bitcoin mining has stopped. ESEA is also in the process of taking all necessary steps internally to ensure that nothing like this ever happens again."

The surreptitious mining was discovered yesterday by an ESEA user.

The company's story about what happened has changed somewhat since then. Initially, ESEA described the mining as a sort of April Fool's prank gone wrong. Yesterday, co-founder Eric Thunberg said that the mining started after a technical glitch occurred with test code that staffers had been toying with. But Levine now says that Thunberg's post was based on incorrect information.

"It was posted based on inaccurate information Eric got at the time," Levine says. "Upon our further investigation, the situation obviously turned out to be more severe that we were initially led on to believe."

In the Bitcoin world, people with access to large compute resources can earn money by adding processing power to the digital currency's peer-to-peer network. It's a business that's become increasingly lucrative and competitive in the past few months as more powerful Bitcoin mining computers have come online.

But the graphics processors found on gaming systems are pretty good at mining Bitcoins, and the ESEA employee did OK for himself. In just a couple of weeks, he netted close to BTC30, or about $3,700.

Without more details, it's hard to say whether ESEA violated the Computer Fraud and Abuse Act, which makes it a crime to intentionally or recklessly cause damage to someone's computer. But there's no question that the secret mining was wrong, says Kurt Opsahl, a senior staff attorney with the Electronic Frontier Foundation.

"This certainly is something they shouldn't have done," he says. "And it's a word of caution to users"

ESEA says it's going to donate its employee's ill-gotten Bitcoin haul to the American Cancer Society and will match the donation from its own funds.

Image: Valve*