Equifax, the credit monitoring agency that lost personal data of 143 million US customers in a massive hack in May, has revealed that it was also the victim of an earlier breach in March.

The earlier breach was serious enough for the company to notify customers, and bring in the information security firm Mandiant to investigate. But the millions of Americans whose personal data the company stockpiles to power its services are not technically customers of the company, and so it did not inform them.

Following a report by Bloomberg, Equifax came clean about the breach in a statement. “Earlier this year, during the 2016 tax season, Equifax experienced a security incident involving a payroll-related service. The incident was reported to customers, affected individuals and regulators. This incident was also covered in the media.”

Specialist blog Krebs on Security was one of the few outlets to cover the breach at the time – when Equifax initially disclosed the hack to customers in May, two months later.

“The March event reported by Bloomberg is not related to the criminal hacking that was discovered on 29 July,” Equifax’s statement continues. “Mandiant has investigated both events and found no evidence that these two separate events or the attackers were related. The criminal hacking that was discovered on 29 July did not affect the customer databases hosted by the Equifax business unit that was the subject of the March event.”



Five organisations are known to have received warnings from Equifax that their data was unlawfully accessed in March, and the company also sent a letter to the New Hampshire attorney general admitting to the breach.

In the letter, the company revealed that the attackers “gained access to the accounts primarily by successfully answering personal questions about the affected employees in order to reset the employees’ pins”. As a result, it was unable to even work out how much fraudulent access occurred, since the logins looked legitimate for its system.

Equifax is already facing criticism for the long delay between the May breach and its revelation to consumers that their data had been stolen, which came four months later. In the intervening period, multiple Equifax executives sold stock in the company, prompting an investigation from US regulators over whether or not they were committing insider trading.

Equifax has always insisted that the executives were unaware of the May breach at the time they sold their stock, but the March breach adds a twist to the tale.

Alongside the 143 million US consumers whose data was stolen, 400,000 UK residents also had their data illegally accessed, Equifax confirmed. Unlike the Americans, however, the Britons only had names, dates of birth, email addresses and telephone numbers stolen – postal addresses or government ID numbers were not included.

On Friday, the company announced that two executives, its chief information officer and chief security officer, would leave the company immediately. It also revealed, on Wednesday, that the root of the breach was a known flaw in the software package Apache. The flaw had been discovered and fixed by Apache in March, but Equifax had not applied the patch to its own systems by May.

The company said its security officials were “aware of this vulnerability at that time, and took efforts to identify and to patch any vulnerable systems in the company’s IT infrastructure”.