It pioneers a ranking system that uses links to assess a website's popularity. Google's simple design is soothing while existing search engines cram their pages with animated adverts.
http://www.sean.co.uk/a/science/history_of_the_internet.shtm
Unleashed by Robert Morris and infects about 6000 computers. Although it causes no physical damage, it clogs up the internet and loses hundreds of thousands of dollars in computer time.
http://www.sean.co.uk/a/science/history_of_the_internet.shtm