Trustwave said on Monday that it has found evidence that the operators of a cybercrime ring known as the Pony botnet have stolen some 85 virtual "wallets" that contained bitcoins and other types of digital currencies. The firm said it did not know how much digital currency was contained in the wallets.

"It is the first time we saw such a widespread presence of this type of malware. It was on hundreds of thousands of machines," said Ziv Mador, security research director with Chicago-based Trustwave.

 

 

Trustwave said it believes the crime ring is still operating, though it does not know who is running the group. The company said it has disrupted the servers that were controlling machines infected with Pony, but expects the group to launch more attacks on virtual currency users.

A representative for the Bitcoin Foundation, a trade group that promotes adoption of the digital currency, did not immediately respond to requests for comment.

Trustwave's discovery comes in the wake of an unrelated cyber attack that spammed bitcoin exchanges earlier this month. That attack prompted at least three online virtual currency traders to halt withdrawals, causing bitcoin's value to plunge 33 percent over three weeks.