Thieves have swiped money from the bank accounts of at least 350 shoppers in Gatineau, Que., and may have stolen sensitive banking information of up to 1,600 people using tampered debit card readers, police say.

Three people were arrested shortly before Christmas in a scam affecting at least eight stores, but the problem continues and there may be many unreported victims, Gatineau police Lieut. Jean-Paul LeMay said at a news conference Thursday.

He would not identify the stores or say how much money was stolen.

LeMay added that the scam is probably carried out by several organized groups of criminals who work in teams to distract store clerks and steal the original card readers while store clerks aren't looking.

"They modify it and they go back and put the modified PIN pad," said LeMay. "And from there they get the information they need to clone cards."

The modified card readers store the card numbers and PINs so the criminals can later download the information, make copies of the cards and use them to withdraw money from bank machines.

Gatineau Chamber of Commerce spokesman Antoine Normand said he feared business will be hurt if customers lose confidence in the popular payment method. He urged stores to be vigilant and install security measures such as camera systems and wires that secure debit card readers to counters. 

René Lapointe, a spokesman for Desjardins financial group, said customers should also guard their cards carefully and change their PIN numbers frequently.

Police released information about the Gatineau debit card fraud just one day after the owner of the Winners and Home Sense retail chains confirmed hackers had broken into a company computer system that stored information about credit and debit card transactions, cheques and merchandise returns.