Pretty much what Loopy said I guess, plus some additional stuff - images or videos of the demons and collaborators, private information about them that can be used to blackmail them, for example. Maybe even figures and statistics for Raptor News, Silver Sacks and Virility, aswell as other companies and organizations that are under demon control.
He might have also stored some more general information about demons there, like what kind of different demons exist, how to take them out, things that are useful for Kat like spells and stuff, etc.
Then there is also the thing that Vergil wrote some kinda security program, if I remember correctly, so I wouldn't wonder if he had put something into it that allows him to spy on everyone using it, constantly collecting data that lands on The Order's servers aswell.