everyone used the same version of the same operating system, a single security hole would let hackers into all the computers. Instead, there’s a multitude of operating systems: Berkeley Unix, AT&T Unix, DEC’s VMS, IBM’s TSO, VM, DOS, even Macintoshes and Ataris. This variety of software meant that no single attack could succeed against all systems. Just like genetic diversity, which prevents an epidemic from wiping out a whole species at once, diversity in software is a good thing.
