Fraudulent activity has been confirmed on the accounts of thousands of Canadian credit-card holders who had their information stolen during a security breach at the U.S. parent company of Winners and HomeSense.

Sources in the financial community confirmed to The Globe and Mail that the number could increase as banks and other credit-card issuers continue to investigate client accounts.

"We have seen fraud on some of those accounts that we can directly link back to the breach," said an official with one card issuer. The man said his company was still in the process of determining how many clients could have been affected by the incident.

About 20 million people shop at the stores, including 2 million Canadians, meaning the retail security breach was one of the biggest in North American history.

The source said card issuers are directly contacting any customers who may have had their information compromised.

Last week, TJX Companies, Inc., announced that their computer systems were hacked late last year, exposing the personal information of millions of customers.

On Wednesday, the Massachusettts Bankers Association said some of the stolen data was used to make purchases in Florida, Georgia, Louisiana and overseas in Hong Kong and Sweden.

Portions of the information regarding credit and debit card sales transactions during 2003 and from the period from mid-May to December 2006 may have been accessed in the intrusion, the company confirmed in their initial press release.

The system that was hacked handles transactions along with cheques and merchandise returns in the U.S., Canada and Puerto Rico. Other regions that could be affected include the U.K. and Ireland.

The RCMP was notified on Jan. 16 by the U.S. Secret Service about a possible breach.

The investigation is being carried out in the U.S. by the Secret Service, but local Canadian police services of jurisdiction will provide help if asked, says the RCMP.

In a statement on the Winners' website, TJX Chairman Ben Cammarata said the company has "engaged two of the very best computer security experts to help us strengthen the security of our systems in order to prevent this from happening again."

"We believe customers should feel safe shopping in our stores."

Spokespeople for Visa and MasterCard said consumers are protected if they are the victims of credit-card fraud. They advised cardholders to watch their statements carefully and notify their card companies if they notice suspicious transactions.

TJX has set up a toll-free help line for Winners and Homesense customers in Canada: 1-866-903-1408