Since some people probably bought it anyway, rejoice about that: concentrate on your customers. Don't inconvenience them. See if you can make it more convenient to buy, for potential conversion.
That's about it, really. Don't try to do something impossible or stupid like trying to take things down off the internet, or trying to make your software uncrackable: neither of those are going to happen and you'll look like a fool (and inconvenience your customers and make enemies) trying.
If this submission's more of a comment on Stack Overflow's well-known propensity to lock every question in the known universe as offtopic or answered, I don't really know what to say to that. ;)
If someone thought your product was good enough to be worth their time to crack it, you must be doing something right. Remember that there are more honest people in the world than dishonest and you won't get the dishonest people to buy your product whatever you do. So concentrate on keeping your honest customers happy.
I think this is the best answer when dealing with such situations. A lot of people make it an ego issue and waste precious time filing DRM complaints, adding checks, etc which not only makes the software bloated but that precious time could be used to add features requested by the paying customers.
Since some people probably bought it anyway, rejoice about that: concentrate on your customers. Don't inconvenience them. See if you can make it more convenient to buy, for potential conversion.
That's about it, really. Don't try to do something impossible or stupid like trying to take things down off the internet, or trying to make your software uncrackable: neither of those are going to happen and you'll look like a fool (and inconvenience your customers and make enemies) trying.
If this submission's more of a comment on Stack Overflow's well-known propensity to lock every question in the known universe as offtopic or answered, I don't really know what to say to that. ;)