There was an interesting article on Slashdot yesterday about Virtual Machine based root kits. Apparently some Microsoft and University of Michigan security researchers have figured out a way to hijack your OS and get it to run on top of a VM. This can be done through any number of unpatched exploits (either existing or future). Suddenly you are running your OS on a VM layer which can be doing any number of things your current scanning software has little chance of detecting. Worth a read and some insight as to what the future may hold for security professionals.