What is the main genre of "hacking" films?

It's a bit more of a buzzword rather than a formal genre, but I think what you are looking for is techno-thriller:

Techno-thrillers (or technothrillers) are a hybrid genre, drawing subject matter generally from science fiction, thrillers, spy, action and war. They include a disproportionate amount (relative to other genres) of technical details on its subject matter (typically military technology); only science fiction tends towards a comparable level of supporting detail on the technical side. The inner workings of technology and the mechanics of various disciplines (espionage, martial arts, politics) are thoroughly explored, and the plot often turns on the particulars of that exploration.

Okay, this answer is strictly subjective.

Firstly, I'm sorry to see this question downvoted and to read Tom's comment with uncalled-for arrogance.

To answer your question, there is no such genre. Currently.

You see, in case of movie subgenres, necessity is the mother of nomenclature. For example, we had horror-comedies for a while. Then 'Shaun of the Dead' happened and suddenly the 'zombie-comedy' entered pop culture. Because that movie influenced a lot of filmmakers all over the world and many more movies of the genre got made. We still don't have vampire-comedies or werewolf-comedies, (though there are movies which fit the bill), simply because the number of movies like that isn't big enough to warrant a subgenre term of their own. And so movies like 'An American Werewolf in London' continue to be called horror-comedies.

Similar is the case with the 'found footage' -- a genre which was virtually non-existent before 'The Blair Witch Project' (exception: 'Cannibal Holocaust from 1980), but then influenced a lot of films in a lot of genres, which include horror ('Paranormal Activity'), zombie ('REC') and disaster ('Cloverfield').

So if some movie centered on hacking comes along which spawns a lot of similar movies, sure, hacking movie could become a genre. It's not now, as the number of such movies isn't big enough. (Off the top of my head, I can only think of 'Hackers' and 'Swordfish'.) Till then, such movies will continue to be classified under other genres.

@tom- I disagree, it's not ridiculous. It's perfectly ordinary for new genres to come up and for one movie to belong to multiple genres. If you can find hackers in all kinds of movies, it would be logical to classify them all under hacker movies should such a genre exist. You can find vampires in horror, romance, and comedy. And it's still called a vampire movie. (Maybe someone should make a movie about vampire hackers!!)

@jonsca- Techno-thriller is a broader term, IMO. And it applies more to novels than movies. Like the works of Michael Crichton and Robin Cook. I never heard anyone describe 'Jurassic Park' the movie as a techno-thriller, even though the book is a prime example of one.