The Kraken ransomware, which targets Windows, Linux/VMware ESXi systems, is testing machines to check how fast it can encrypt data without overloading them.

According to Cisco Talos researchers, Kraken’s feature is a rare capability that uses temporary files to choose between full and partial data encryption.

The Kraken ransomware emerged at the begining of the year as a continuation of the HelloKitty operation, and engages in big-game hunting attacks with data theft for double extortion.