No need for stocking masks and sawn-off shotguns.

The unprecedented heist of $81 million from the U.S. account of Bangladesh's central bank is the latest among increasingly large thefts by criminals who have leveraged the speed and anonymity of hacking to revolutionize burgling banks.

Hundreds of millions of dollars, and perhaps much more, have been stolen from banks and financial services companies in recent years because of this alliance of traditional and digital criminals, with many victims not reporting the thefts for fear of reputational damage.