The U.S. parent company of Winners and HomeSense announced Wednesday that a security breach they thought was confined to just a few months is bigger than they first thought.

While TJX previously believed the intrusion took place only from May 2006 to January 2007, it now believes its computer system was also intruded upon in July 2005 and on various other dates in 2005.

It says that information regarding portions of credit and debit card transactions at its U.S., Puerto Rican and Canadian stores from January 2003 through June 2004 was compromised.

The company had previously reported that the 2003 transaction data had potentially been accessed.

It adds that debit card transactions with cards issued by Canadian banks are excluded from the breach.

For most of the transactions from September 2003 through June 2004, some of the card information was "masked" at the time of the transaction, making that portion unavailable to the intruder.

TJX says it continues to believe there was no compromise of customer data after mid-December 2006.

Carol Meyrowitz, President and CEO of TJX personally apologized for the inconvenience.

"Our investigation is ongoing, and we are providing an update today on new developments," she said in a news release on the company's website.

"We are dedicating substantial resources to investigating and evaluating the intrusion which, given the nature of the breach, the size and international scope of our operations, and the complexity of the way credit card transactions are processed, is, by necessity, taking time."

"Based on everything we have done, I believe customers should feel safe shopping in our stores," she added.

About 20 million people shop at TJX stores, including 2 million Canadians who shop at Winners and HomeSense, making the security breach one of the biggest in North American retail history.

TJX Companies previously announced in January that their systems were hacked late last year, exposing the personal information of millions of customers.

TJX has created toll-free helpline numbers in the U.S., Canada, the U.K., and Ireland to assist customers with concerns about this issue:

In Canada: Toll-free help line: 1-866-903-1408