True. I should have asked for one OS that connects to the Internet. :-)
Actually, I did get a virus while using DOS 3.0. It was a “Boot Virus”, on a 5-1/4 inch floppy disk. Ask your grandfather what a 5-1/4 inch floppy disk is. The virus would attach to the boot sector of the floppy disk, and could propagate to any other floppies installed after the PC was infected. These floppies would then infect subsequent PCs that they were inserted in. The infection occurred on startup of the PC with the floppy, often inadvertantly, left in the drive. The PC manufacturers quickly added code to the BIOS that would detect and warn of a pending infection.