The Top 100 Hoaxes - here's #40:

Internet Spring Cleaning
In 1997 an email message spread throughout the world announcing that the internet would be shut down for cleaning for twenty-four hours from March 31 until April 2. This cleaning was said to be necessary to clear out the "electronic flotsam and jetsam" that had accumulated in the network. Dead email and inactive ftp, www, and gopher sites would be purged. The cleaning would be done by "five very powerful Japanese-built multi-lingual Internet-crawling robots (Toshiba ML-2274) situated around the world." During this period, users were warned to disconnect all devices from the internet. The message supposedly originated from the "Interconnected Network Maintenance Staff, Main Branch, Massachusetts Institute of Technology." This joke was an updated version of an old joke that used to be told about the phone system. For many years, gullible phone customers had been warned that the phone systems would be cleaned on April Fool's Day. They were cautioned to place plastic bags over the ends of the phone to catch the dust that might be blown out of the phone lines during this period.