For example, a battalion of bots, after taking over unsuspecting computers, might enter an online casino game room, pretending to be real people. The criminal controlling the bots gives each a small amount of dirty money – usually acquired from stolen credit cards or illicit drug sales.

The bots are programmed to wager a certain amount, pick cards and fold if necessary. Then the criminal, or so-called bot master, takes the only seat left, easily winning the fixed game.

After several rounds, the bot leader cashes out and gets a check or wire transfer from the online casino"s payment processor. And the bank, without doing significant digging, is none the wiser.

These laundering botnets can leave banks running afoul of regulations on money laundering, but that isn't the only problem for banks according to the report:

Bots can damage a bank more directly by infecting a computer at the institution itself, Furst said. When that happens, the bots communicate all of the passwords and identity information on the computer or even the entire network.

One bank chief security officer told Furst that a bot took over a computer at his institution in the United States and tried to wire tens of thousands of dollars to Britain.

The bank only discovered the transaction when the British bank officer called the U.S. branch to verify the transaction.