The POS breach that struck 216 Jimmy John's restaurants impacted 108 other restaurants as well, according to PC World. Many of the targeted restaurants were independents and pizza concepts.

The restaurants are all customers of POS provider Signature Systems.

Signature Systems was alerted to the breach on July 30, but it may have started around June 16. The malware was removed from most machines within a week and the attacks have been blocked.

The malware was installed by hackers who gained access to the terminals, which are remotely managed by Signature Systems, with usernames and passwords. Hackers were able to steal cardholders' names, card numbers, expiration dates and verification codes from the cards' magnetic stripes.