The Mokes malware was discovered earlier this year on Windows and Linux, but researchers from Kaspersky have found an OS X variant. It can steal virtually any data from any machine, including using the webcam and microphone, recording keystrokes, taking documents, and watching the screen.
The malware is known as Backdoor.OSX.Mokes. Once it establishes itself on the victim's Mac, it sets up an encrypted link with a server for communication, making it more difficult to spot. It also establishes a number of backdoors, making it hard to remove.
There's no official response from Apple yet, but hopefully a patch will be in the works. Kaspersky is advising users to delete the binary if they find it on their machine, although given the backdoors it reportedly installs, that might not be enough to keep Mac users totally safe.
Backdoors in OS X used to be far more rare, but several different pieces of malware have popped up in the last few months. It's as good a time as any to make sure that users have a backup of all their important documents, easy to do with Apple's Time Machine software and a cheap external hard drive.