U.S. consulting firm Greylock McKinnon Associates disclosed a data breach in which hackers stole as many as 341,650 Social Security numbers.

The data breach was disclosed on Friday on Maine’s government website, where the state posts data breach notifications.

In its data breach notice sent by mail to affected victims, GMA said it was hit by an unspecified cyberattack in May 2023 and “promptly took steps to mitigate the incident.”

GMA provides economic and litigation support to companies and U.S. government agencies, including the U.S. Department of Justice, bringing civil litigation. According to its data breach notice, GMA told affected individuals that their personal information “was obtained by the U.S. Department of Justice (“DOJ”) as part of a civil litigation matter” supported by GMA.

The reasons and target of the DOJ’s civil litigation are not known. A spokesperson for the Justice Department did not respond to a request for comment.

GMA said that individuals notified of the data breach are “not the subject of this investigation or the associated litigation matters,” and that the cyberattack “does not impact your current Medicare benefits or coverage.”

“We consulted with third-party cybersecurity specialists to assist with our response to the incident, and we notified law enforcement and the DOJ. We received confirmation of which individuals’ information was affected and obtained their contact addresses on February 7, 2024,” the firm wrote.

GMA told victims that “your personal and Medicare information was likely affected in this incident,” which includes names, dates of birth, home address, some medical information and health insurance information, and Medicare claim numbers, which included Social Security Numbers.

It’s unclear why it took GMA nine months to determine the extent of the breach and notify victims.

GMA, and the firm’s outside legal counsel, Linn Freedman of Robinson & Cole LLP, did not immediately respond to a request for comment.