What was the first computer bug and when did computer viruses first appear?

Grace Hopper found a moth had landed in between the solenoid contacts in the Mark II Calculator, a massive analog computer at Harvard University, designed by Howard Aiken. She removed the squashed moth and annotated her log book with an entry (along with the moth fastened to the page) that referred to the first "computer bug." Computer viruses became a problem in the 1980s as DOS based computers began to proliferate. The file structure utilized by these machines made it relatively easy in 1986 for the maker(s) of the "Brain" virus to play havoc with the boot sectors on floppy disks. In 1988, an anti-virus program was devised to remove Brain from infected floppies.  more