It's just been disclosed that a hacker stole sensitive data from computer systems used by TJX, parent company of retailers TJ Maxx and Marshalls.  HomeGoods, A.J. Wright, Winners and HomeSense stores, all subsidies of TJX, may also be affected.

The hackers targeted systems which TJX uses to handle credit and debit transactions for stores in the U.S. and Puerto Rico, but the company admits its still investigating the full depth of the compromise.

TJX representatives said the security breach occurred sometime in May, but the compromise continued until mid-December.  The unauthorized intrusion was initially detected by the company sometime in December but only publicly revealed last week.

Visa USA is providing help to the banks of all affected customers.  The Bank of America and American Express are also watching accounts that may be used for fraudulent transactions.  TJX has established a helpline for all customers who have questions or concerns about the incident: 866-484-6978 in the United States, 866-903-1408 in Canada and 0800-77-90-15 in the United Kingdom and Ireland.

TJX has not disclosed how many customers were left vulnerable from the security breach, though it states that transactions it knows are compromised occurred between May and December 2006 and transactions in 2003.

TJX urges customers to check their bank transactions for irregular behavior.