A Lawrence resident is among 20 Commerce Bank customers whose personal account information was compromised last week during a hacking of a bank computer system, a bank spokeswoman said Tuesday.

The 20 customers had their personal information – including account numbers, Social Security numbers, dates of birth, addresses and mothers’ maiden names – accessed by the hacker or hackers who gained entry into a database maintained in Kansas City, Mo., said Paula Oakman, a spokeswoman for the Kansas City, Mo.-based bank.

Affected account holders have been notified by mail.

The database contained information for 3,000 accounts, she said, but there is no indication that other account information had been accessed. All are being provided with free credit-monitoring services for two years.

“They’re not going to be responsible for any charges, at all,” she said.

The hacking was discovered by the bank’s fraud-detection software and the illegal activity was cut off immediately, Oakman said.

“We’re carefully and actively monitoring all accounts for fraudulent activity, and we employ sophisticated fraud-detection software,” she said. “We’ve taken the necessary steps to update our security system based on this new type of threat to our system.”

The Federal Bureau of Investigation is conducting an investigation out of the FBI office in St. Louis. Commerce has corporate offices in St. Louis and Kansas City, Mo.

“We were notified by Commerce of a situation and we’re coordinating an investigative effort, obviously, with Commerce people,” said Peter Krusing, an FBI spokesman in St. Louis. “It’s an ongoing investigation.”

Commerce Bancshares Inc. is a $15.5 billion regional bank holding company that operates Commerce Bank N.A., which has 360 banking locations in Kansas, Missouri, Illinois, Oklahoma and Colorado. Commerce has six locations in Lawrence.