A Hacker (ハッカー Hakkā?) is someone with the ability to force an item, program, or system to deviate from its intended functions for the hacker's own ends. In the context of the Digimon franchise, where Digimon inhabit a world birthed from electronic systems, hackers can have significant power to influence the Digital World, from uninvited access to actual, reality-warping effects.
A malicious hacker once managed to disrupt the Computer Network, and it was still being repaired when Coelamon was discovered, while the evil feelings of hackers who abuse the Network produced Devidramon.
Digital Monster Ver.S: Digimon Tamers
Digimon WorldAnalogman is a hacker.
Digimon Digital Card Battle
A is a hacker who is able to force entry in the world by hacking VenomMyotismon. He is confronted and challenged by the Protagonist to a Card Battle, but he uses his abilities to cheat in a duel, allowing him to draw whatever cards he wishes and to send the Protagonist's cards to the bottom of the deck. The threat of his hacking skills when combined with his evil nature is so great that, in the end, Rosemon is forced to quarantine both herself and A in the Net to stop him.
The concept of "Hacker Tamers" exists.
Digimon Story: Cyber Sleuth