BOSTON (AP) – At least 45.7 million credit and debit card numbers of TJX Cos. customers were stolen from the discount retailer’s computer system over several years, according to a regulatory filing by the company Wednesday.

The filing with the Securities and Exchange Commission gave the first detailed account of the breach that the company initially disclosed in January.

It also said another 455,000 customers who returned merchandise without receipts had their personal data stolen, including driver’s license numbers.

TJX owns T.J. Maxx, Marshall’s and other stores in North America and the United Kingdom. There is a T.J. Maxx store in Auburn.

TJX spokeswoman Sherry Lang did not immediately return a message from The Associated Press seeking comment late Wednesday.

But Lang told The Boston Globe, which first reported the filing Wednesday night, that about 75 percent of the compromised cards either were expired or had data in the magnetic stripe masked, meaning the data was stored as asterisks, rather than numbers.

Lang said the extent of the damage may never be known because of the methods used by the intruder as well as file deletions made by TJX in the normal course of business.

“There’s a lot we may never know and it’s one of the difficulties of this investigation,” Lang said. “It’s why this has taken this long and why it’s been so tedious. It’s painstaking.”

Avivah Litan, vice president of research and advisory company Gartner Inc., told the Globe the TJX breach is “the biggest card heist ever.”

“This was obviously done over a long period of time, in many locations,” she said. “It’s done considerable damage.”

Police charged six people in Florida last week with using credit card numbers stolen from a TJX database to buy about $1 million in merchandise with gift cards.

In Wednesday’s filing, TJX said for the first time that Dec. 18, 2006, was the date it first learned that there was suspicious software on its computer system.

TJX said it believes hackers invaded its systems in July 2005, on later dates in 2005 and also from mid-May 2006 to mid-January 2007. The company said no customer information was stolen after Dec. 18, one day before it hired General Dynamics Corp. and IBM Corp. to investigate. By Dec. 21, those investigators determined that the computer systems had been intruded and that an intruder remained on the systems.

TJX said it notified federal authorities Dec. 22, and on Jan. 3, TJX officials and Secret Service agents met with banks and payment card and check processing companies to discuss the computer intrusion.

Framingham-based TJX is facing an investigation by the Federal Trade Commission and lawsuits from individuals and banks accusing it of failing to do enough to safeguard private data and of delaying disclosure of the problem.