POS malware may come in three types: keyloggers, memory dumpers, and network sniffers. Criminals behind the proliferation of this type of malware are mainly after data they can sell, not for personal use. 2014 was dubbed by industry experts as the Year of the Largest Retail Hacks thanks to POS malware. Businesses that are unknowingly using affected POS machines must contain the infection by disconnecting from the network and then conduct an audit to determine which terminals are infected and which ones are not.”]
Source: https://blog.malwarebytes.com/threats/point-of-sale-pos/