Conficker, which was set to activate on April 1 but failed to cause any problems, isn't the first virus to be programmed to take action on a certain date or time. Experts believe that worms with a trigger date can lead to panic and hype. Here are some others:
Jerusalem One of the first known viruses, dubbed Jerusalem, was first detected in the Israeli city in October 1987 and targeted at DOS systems. It was programmed to delete programs on Friday 13th, except in the year 1987.