Credit card skimmers were found on payment machines at five Primark locations across the Northeast, according to store officials.

Primark said credit cards could have been compromised as early as July 29, leaving criminals almost three months to access customers’ personal payment information.

The discount fashion retailer doesn’t believe all card transactions were affected and Primark contacted police on Oct. 17 when the devices were discovered, Philly Voice reported.

Stores at King of Prussia and Willow Grove malls, as well as at Downtown Crossing in Boston, Danbury Fair Mall in Connecticut and Freehold Raceway Mall in New Jersey were affected.

Credit card skimmers are devices that fit discreetly over card readers in order to read and stream information when a card is used to make purchases. The devices are almost impossible to detect for the average consumer. Simple card skimmers do not work on EMV chip cards, but as of yet, it is unknown what type of skimming devices were used, pymnts.com reported.

Primark encourages shoppers who used a debit or credit card at affected stores to monitor their billing statements.

RELATED: Primark department store to open Thursday in Downtown Crossing

The Dublin-based retailer opened its first U.S. stores last fall and is poised for a stateside expansion.