Major U.S. banks came under growing pressure from banking regulators to improve the security of customer account information after Citigroup Inc. became the latest high-profile victim of a large-scale cyber attack, Reuters reported.

Though Citigroup insisted the breach had been limited, experts called it the largest direct attack on a major U.S. financial institution and forecast it could drive momentum for a systematic overhaul of the banking industry’s data security measures.

The Federal Deposit Insurance Corp. (FDIC) is developing new guidance for banks and may ask “some banks to strengthen their authentication when a customer logs into online accounts,” FDIC Chairman Sheila Bair said.

Citibank said computer hackers breached into the bank’s network and accessed the data of about 200,000 bank card holders in North America. The bank waited more than a month before making the full extent of the breach public, drawing criticism from lawmakers and lawyers.

Citigroup is the latest in a growing list of companies that have suffered cyber attacks, including Sony Corp. and Google Inc.

Security experts said the attack may be a watershed moment for the U.S. banking industry, which until now had suffered fewer direct hacker attacks than retailers.

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