The rash of e-commerce sites infected with card-skimming malware is showing no signs of abating. Researchers on Thursday revealed that seven sites—each with more than 50,000 collective visitors per month—have been compromised with a previously unseen strain of sniffing malware designed to surreptitiously swoop in and steal payment card data as soon as visitors make a purchase.

One of those sites, UK sporting goods outlet Fila.co.uk, had been infected since November and had only removed the malware in the past 24 hours, researchers with security firm Group-IB told Ars. The remaining six sites—jungleeny.com, forshaw.com, absolutenewyork.com, cajungrocer.com, getrxd.com, and sharbor.com—remained infected at the time this post was being reported. Ars sent messages seeking comment to all seven sites but has yet to receive a response from any of them.

Group-IB has dubbed the JavaScript sniffer GMO after the gmo[.]il domain it uses to send pilfered data from infected sites, all of which run the Magento e-commerce Web platform. The researchers said the domain was registered last May and that the malware has been active since then. To conceal itself, GMO compresses the skimmer into a tiny space that’s highly obfuscated and remains dormant when it detects the Firebug or Google Developer Tools running on a visitor’s computer. GMO was manually injected into all seven sites, an indication that it is still relatively fledgling.