TGT Target Corp

By Ryan Tracy 

WASHINGTON--U.S. regulators are warning of a pattern in cyberattacks targeting automated teller machines that could saddle banks with "large dollar losses" from unauthorized withdrawals.

The attacks are increasing, senior bank supervisors on the Federal Financial Institutions Examination Council said in a statement Wednesday. They said small- and midsize banks are especially at risk.

The warning is the latest evidence that hackers are exploiting weaknesses in the security of the U.S. financial system for illicit profits. In recent months, banks have been reissuing millions of credit cards as a result of stolen customer information at Target Corp. and other retailers.

Write to Ryan Tracy at ryan.tracy@wsj.com

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