OSX/HellRTS is a Remote Access Trojan (RAT) targeting Mac OS X by posing as an innocent file. Once installed, the trojan has virtually complete control of the computer and can steal information, download additional files, and spy on the users. Variants were discovered as early as 2005 [1]. This was the first XProtect signature to be silently added as part of a Snow Leopard update, specifically to version 10.6.4 [2].

References:

1. https://www.securemac.com/osx/trojan-horse-alert-hellraiser-aka-osxhellrts-d
2. https://www.macstories.net/news/os-x-10-6-4-updates-anti-malware/