A mysterious piece of malware that gives attackers surreptitious control over webcams, keyboards, and other sensitive resources has been infecting Macs for at least five years. The infections—known to number nearly 400 and possibly much higher-remained undetected until recently and may have been active for almost a decade. Fatrick Wardle, a researcher with security firm Synack, said the malware is a variant of a malicious program that came to light in January after circulating for at least two years. Dubbed Fruitfly by some, both malware samples capture screenshots, keystrokes, webcam images, and information about each infected Mac. Both generations of Fruitfly also collect information about devices connected to the same network. After researchers from security firm Malwarebytes discovered the earlier Fruitfly variant infecting four Macs, Apple updated macOS to automatically detect the malware.

The variant found by Wardle, by contrast, has infected a much larger number of Macs while remaining undetected by both macOS and commercial antivirus products. After analyzing the new variant, Wardle was able to decrypt several backup domains that were hardcoded into the malware. To his surprise, the domains remained available. Within two days of registering one of the addresses, close to 400 infected Macs connected to the server, mostly from homes located in the United States. Although Wardle did nothing more than observe the IP address and user names of Macs that connected to his server, he had the ability to use the malware to spy on the users who were unwittingly infected.