A botnet of infected point-of-sale (POS) systems is behind the compromise of more than 20,000 payment cards since August, reports have found.

On Wednesday, Ars Technica published an article on the threat, which was detected by Los Angeles-based security firm IntelCrawler. According to the company, the targeted POS systems were infected with a variant of Dexter, called “Stardust.”

The Stardust malware iteration was also found to be used in another recent campaign to steal credit card data in the U.S. and abroad. Arbor Networks detailed those attack activities in a Tuesday report.

In this campaign, researchers found that botnet operators controlled 31 machines belonging to U.S. restaurants and retailers, Ars reported. IntelCrawler has yet to determine fraudsters' means of infecting POS systems.