Datamon is a ultimate level, virus type, machine attribute Digimon. It's name is derived from data and monster. It was once a vaccine Digimon, then it got infected by a virus Digimon, making it a virus type. It's one of the smallest Ultimates.
For some odd reason Datamon is a Season 1 of the Anime although its first game was Digimon World 2, and its first Nintendo Game was Digimon World Dawn & Dusk. In the anime it caused the DigiDestined troubles.