Malicious web code that Magecart groups use to steal payment card data from online stores is bustling business on underground forums. There are at least 38 unique families of such scripts, some more advanced than others, but each has multiple custom variants. Group-IB, a security outfit specialized in detecting and preventing cyber attacks, analyzed 15 of the 38 JS-Sniffer families. An estimated 1.5 million unique visitors land on those sites on a daily basis; this does not reflect the number of victims.
Source: https://www.bleepingcomputer.com/news/security/dozens-of-credit-card-info-skimming-scripts-infect-thousands-of-sites/