A major U.S. hacker agreed to plead guilty to federal charges linked to electronic break-ins at 7-Eleven Inc and a chain of New England grocery stores, a court filing shows.

The plea by Albert Gonzalez could wrap up a large federal effort against what prosecutors have painted as the biggest data breach ring caught to date. The ring has been accused of stealing payment card data from millions of customers of merchants, including TJX Cos Inc and BJ's Wholesale Club Inc.

Government prosecutors have described Gonzalez, of Miami, as the ringleader of a gang responsible for the attacks. Gonzalez's attorney denied he played such a role, but Gonzalez had already agreed to plead guilty to charges in Massachusetts in connection with those break-ins.

Now, according to a December 2 court filing, Gonzalez also has agreed to plead guilty in connection with federal charges he faced in New Jersey. There he had been tied to electronic break-ins at New England grocer Hannaford Brothers Co, a unit of Delhaize Group, and at 7-Eleven Inc, the convenience store chain.

All the break-ins have raised questions about the effectiveness of efforts to improve payment-card security against hacking attacks and revealed splits among banks, merchants and payment networks over which should bear the costs of upgrades.

The court filing did not give details about the plea agreement and Justice Department officials declined to comment. An attorney for Gonzalez was not immediately available.

The new guilty plea was reported earlier today by the Boston Globe newspaper. In the Massachusetts matter alone, Gonzalez faced up to 25 years in prison in connection with the attacks, which would be among the stiffest ever in a hacking case.

(Reporting by Ross Kerber; editing by Andre Grenon)