"Porygon is capable of reverting itself entirely back to program data and entering cyberspace. This Pokémon is copy protected so it cannot be duplicated by copying."
Pokemon can come from anywhere. From the skies, to the seas, to space, and apparently, even Cyberspace. There's some debate as to whether Porygon was created in a computer by a human or it just created itself. Fun fact, the only episode that featured Porygon in the anime was banned from coming to the US. Why? Because it was a cyberspace themed episode, and the bright flashes of light caused kids in Japan to have seizures.
Porygon's Basic Attacks are Tackle and Quick Attack, while its Special Attacks are Signal Beam, Psybeam, and Discharge.