Videotex systems were once thought of as the way normal people would get around to using computers, but so far, no service calling itself videotex has made it into the big time. Virtual memory, which requires a PMMU, is a feature of System 7, available via a control panel, or it can be utilized via third-party software. Some memory-hungry programs, such as Photoshop, have their own virtual memory schemes. Virtual memory is best reserved for programs you occasionally run that need more RAM than you have. Viruses have sub-species named for the way they operate, such as worms and Trojan horses.
Viruses travel from computer to computer via floppy disks, networks and modems.
You'll know you have a virus when things start acting funny on your computer. If you can suspect a virus, get virus-protection software and disinfect your hard drive and every single disk in your house and office. Then never let anyone put a disk into your computer without checking it first. The best package is one called Disinfectant. He rewrites the program every time a new virus is discovered.