(Bloomberg) -- Lloyds Banking Group Plc was hit by a cyber attack that disrupted online services for customers two weeks ago, a person with knowledge of the matter said, amid mounting concern over the threat hackers pose to major banks.

Britain’s largest mortgage lender was targeted by a denial-of-service attack, which aims to cripple an online system by flooding it with traffic, said the person who asked not to be identified because the details aren’t public. To defend its systems, Lloyds used geo-blocking tactics to prevent web requests from servers in locations used in the assault and scrubbing techniques to cleanse incoming data, the person added.

Britain’s biggest banks have been hurt by a string of outages, some attributed to obsolete software and others to malicious activity by hackers, prompting lawmakers to call for more spending on technology and closer supervision of computer systems by board members. The Bank of England has also identified cybercrime as a serious threat to the resilience of the banking system.

“We had a normal service in place for the vast majority of this period and only a small number of customers experienced problems,” Lloyds said in an e-mailed statement referring to the outages from Jan. 11 to 13. “We will not speculate on the cause of these intermittent issues.” The Financial Times reported the incidents as cyber attacks earlier on Monday.

Although denial-of-service attacks are relatively common, many banks refuse to say publicly if they have been hit. HSBC Holdings Plc broke ranks a year ago when it said it was targeted by a such an assault that caused problems for some U.K. customers. Lloyds, which has said it has the most mobile banking customers in Britain, is among major lenders investing billions of pounds in technology and cyber security as consumers increasingly move online.

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