A VMWare cofounder says virtual appliances that run apps alone could threaten operating systems.The virtual appliance model could be a major threat to operating systems from major vendors such as Microsoft Corp., says a cofounder of VMWare Inc. Mendel Rosenblum told an audience at the LinuxWorld Conference & Expo in San Francisco last week that a virtual appliance, which bundles a software application with only the operating system code needed to make it run, can then be deployed on a virtualized server regardless of the host operating system. Rosenblum is also chief scientist of virtualization at VMware.