Hackers have been stealing credit card details in Magento and other ecommerce-based websites. The swiper code was found in a Magento core file: Cc.app/code/core/Mage/Payment/Model/Method/Cc.php. The file had been modified recently compared to the rest of the files in that directory. The source code behind the image appears overwhelming and cryptic. Below all of the legitimate image source code is a long list of stolen credit card numbers.”]
Source: https://blog.sucuri.net/2016/10/magento-credit-card-swiper-exports-image.html