Last week, Russian anti-virus firm Doctor Web disclosed a newly discovered piece of OS X malware known as Mac.BackDoor.iWorm that at the time had affected roughly 17,000 machines around the world. While the exact mechanism of infection was unclear, an interesting twist to the story involves compromised machines running search queries on Reddit to obtain instructions about which command and control servers should be used to manage the botnet.
Once connected to a command and control server, the backdoor opened by the malware on the user's system can receive instructions to perform a variety of tasks, from stealing sensitive information to receiving or spreading additional malware.
In an effort to address the threat, Apple has now updated its "Xprotect" anti-malware system to recognize two different variants of the iWorm malware and prevent them from being installed on users' machines.
You can read more about it at MacRumors.com