FRAMINGHAM, Mass.-based retailer TJX Companies, which operates T.J. Maxx, Marshalls and other stores, warned customers that its computer network has been broken into, compromising customer credit-card information and other data.

In a letter posted on the TJX Web site today, company founder and chairman Ben Cammarata wrote of his disappointment about the discovery of the unauthorized intrusion into the company’s network, and said an investigation is ongoing to understand its consequences more fully. TJX has set up toll-free phone numbers in the United States, Canada, the United Kingdom and Ireland to take questions from customers about the security incident.

“I can tell you that we were extremely disappointed when we determined that we have suffered an unauthorized intrusion into our computer systems that process and store information related to customer transactions,” Cammarata stated in the public letter. He noted: “While there is much we still have yet to understand about this issue, I can assure you that we are taking steps to safeguard confidential information and working closely with law enforcement in the U.S., Canada and the U.K. so that those responsible for this act will be brought to justice.”

In a separate statement, TJX said it discovered the intrusion into its systems for processing credit, debit and returns in mid-December 2006 and immediately notified law enforcement. TJX added that “it immediately engaged General Dynamics and IBM,” hiring them to “monitor and evaluate the intrusion, assess possible data compromise, and seek to identify affected information.” The two vendors are also expected to help TJX upgrade its systems.

TJX so far has determined that the intrusion involves computers pertaining to its T.J. Maxx, Marshalls, HomeGoods and A.J. Wright stores in the United States and Puerto Rico, and its Winners and HomeSense stores in Canada. While it has not yet confirmed further penetration in its network, TJX suspects intruders also may have breached systems related to its T.K. Maxx Stores in the United Kingdom. and Ireland and its Bob’s Stores in the United States.

As part of the statement, TJX also noted the company “does not yet have enough information to estimate the extent of the financial cost it will incur as a result of the situation.”