Tim Davis, president of The UPS Store, apologized in a statement for any anxiety the theft may have caused customers. He said the company had deployed "extensive resources to quickly address and eliminate this issue."
Each UPS Store is franchised and runs separate computer systems, which may have helped limit the extent of the attack. UPS said the bug was not found at any of its other businesses.
The UPS breach is the latest in a long string of incidents in which hackers have made off with retail consumer data.