Corrected entry: If you remember the reason why O'Connor was misdirected to the last scene facility was that there wasn't a master server where the Skynet was installed so this means that Skynet was the virus that spread to all computers in Earth. When Skynet fired the ICBM's (Nuclear Missiles) at the major cities on the planet it actually committed suicide. If Skynet destroys the cities, it destroys the computers the had the virus and consequently itself.
Phil Watts
30th Aug 2003
Correction: Destroying major cities would wipe out a large percentage of computers, not every computer. Skynet would still be able to operate on the millions of remaining computers around the globe.
Phil Watts