Investigators are examining possible computer breaches at as many as 12 banks linked to Swift's global payments network that have irregularities similar to those in the theft of $81 million from the Bangladesh central bank, according to a person familiar with the probe.

FireEye, the security firm hired by the Bangladesh bank, has been contacted by the other banks, most of which are in Southeast Asia, because of signs that hackers may have breached their networks, the person said. They include banks in the Philippines and New Zealand but not in Western Europe or the United States. There is no indication of whether money was taken.

The expansion of the investigation four months after the discovery of the Bangladesh attack, the biggest known cyber-heist in history, suggests a broad and serious campaign to breach the international financial system.