Steps were immediately taken to remove the tampered card readers in the affected stores, the company said in a news release.
"We are not aware, nor have we been notified of any reports that customer accounts were compromised," the company said in a release.
Besides Mountain View, the affected Lucky stores are in Sunnyvale, Pinole, Milpitas, Redwood City, El Cerrito, Daly City, Foster City, San Carlos, Millbrae and Alameda, as well as one in Santa Clara, one in San Francisco, two in Fremont and four in San Jose.
The suspected card skimming also was reported at a Save Mart store in Watsonville.
Alicia Rockwell, the company's director of public affairs, said a couple of Lucky store employees reported incidents at the Lucky store in Petaluma over the weekend, but the self-checkout readers and those at checkouts staffed by employees were clean.
The skimming devices that are installed in the card machines capture credit card numbers and debit card pin numbers. Identity thieves then make transactions on those cards.
The company first learned about the problem around Nov. 11 and sent out a Consumer Advisory on Nov. 23, Rockwell said.
The compromised machines were found in the 21 stores when all 233 stores in Northern California and Northern Nevada were checked, Rockwell said.
Stephen Ackerman, chief financial officer of Save Mart, said today the company expects to learn this week the starting and ending dates of the credit and debit card reader tampering.
The company has had the full support of local, state and federal authorities, financial institutions and card processors, Ackerman said.
"At this time, we strongly recommend that anyone who used our self-check terminals in the affected stores during the months of October and November consider closing their bank account and opening a new one," Ackerman said.
Authorities say the thefts are most likely to occur over the weekend when most financial institutions are closed or have limited hours.
Customers with compromised account statements should contact the Lucky Customer Support Center at (800) 692-5710.
Save Mart operates 233 stores in Northern California and Northern Nevada under the Save Mart, S-Mart Foods, Lucky and FoodMaxx banners.
— Bay City News Service