In Pictures: Geeky ways to celebrate Friday the 13...
Beware the Friday the 13th Virus (if you still use DOS)
The Jerusalem virus, first detected in Jerusalem in 1987, was a DOS virus that infected executable files like crazy and included a destructive payload set to go off on Friday the 13th in every year except for 1987 and destroy all program files executed. The virus did in fact do damage.
In Pictures: Geeky ways to celebrate Friday the 13th