In late 2013, an A.T.M. in Kiev started dispensing cash at seemingly random times of day. No one had put in a card or touched a button. Cameras showed that the piles of money had been swept up by customers who appeared lucky to be there at the right moment.
The majority of the targets were in Russia, but many were in Japan, the United States and Europe.
No bank has come forward acknowledging the theft, a common problem that President Obama alluded to on Friday when he attended the first White House summit meeting on cybersecurity and consumer protection at Stanford University. He urged passage of a law that would require public disclosure of any breach that compromised personal or financial information.