In 2010, this little ditty arrived on the scene in the form of proof-of-concept malware, and it's arguable as to whether HellRTS.D actually made it out into the wild. The bug, which actually targeted both Macs and PCs, could open a back door that would grant access to hackers who might be looking longingly at your data. It was also designed to replicate and rename itself for the added ability to slip through the cracks. But its effects would have been limited based on the fact that it required physical access to the targeted machine. Its threat was further limited by Apple, a short time after it was discovered, when the company built preventative features into Snow Leopard.