Well, this is kind of late, since technically the anniversary was yesterday, but I didn't get a chance to make a complete thread about it. Anyway, on to the subject I know you're all dying to know about!

On March 6th, 1991, the launch of a computer virus named the Michelangelo Virus started infecting user's PC's at random. Though the virus's coding had nothing to do with the famous artist, it was named after him because it was launched on the anniversary of his birthday.

It targeted the hard disk (the place where all you computer's information is stored, otherwise known as "hard drive", "disk drive", "hard disk drive", you get the idea) essentially blocking user's stored information. So when someone tried to insert a floppy disk (what are those?!! Pretty much akin to today's CD's), the computer wouldn't be able to detect it, which obviously caused many problems for computer users. In 1992, it was reported that 10,000-20,000 computers had lost information in result.

This virus was one of the earliest ones to receive media attention! It was quickly advised that users shouldn't use their PC's on March 6th anymore in fear of losing their information, because it seemed to be an annual re-occurrence. Though it caught a lot of attention, the media quickly lost interest and it was soon forgotten not a couple of years after it was discovered. Luckily by 1997, though the virus was good about avoiding detection, all traces of the virus had been deemed purged out of the wild and it hasn't flared up since (to our knowledge).

If you'd like to read more:

The Virus Wiki