I cannot even read this thread in its entirety. Yes, you absolutely should break his computer. That, is, if you want him to NEVER trust you again, possibly push him off the derech, and have him consider suing you (and in civil court at least, you would probably be liable).
Whether or not it is right for him to have a computer, that he bought, with HIS OWN MONEY, you are not dealing with someone who i.e., bought illegal drugs (which I believe should be flushed down the toilet by parents if they find them). Though computers have downsides to them, they can have very positive aspects of usage, as well, and that is what should be emphasized IMO. Don’t cause irreparable harm by an impulsive action. Talk to your son, express your feelings, and then examine those feelings. Perhaps he can be made to understand your concerns. And find wholesome ways for him to utilize this device, which really can eb amazing when used in the right way, like so many other things that we use every day.