Congratulations! Having cracked versions out there indicates that your software is both useful and notable, which is a point where many developers would love to arrive at, maybe, one day. As to what to do about it, there are two basic tracks, neither of which is incompatible with the other: 1. The legal route: notifying distribution sites that they're hosting content in violation of copyright law, requesting takedown…
There is a third option which I'm surprised no one has mentioned so far: Ignore them. First, people or companies using the cracked version of your software were never going to buy it. These people do not pay for software, and nothing you do will convince them to pay for it. Secondly, whatever measures you put in place to combat the cracked versions will potentially have a negative impact on your actual paying users -…
I have pirated person when I was a poor student where it literally was money for food vs buying some software. I buy all my (commercial) software now that I can easily afford it and support multiple open source projects with donations. And the software houses, Bands and filmers who have seen the most of my money have been precisely the ones whose work I liked before.
The creators who have not been assholes about it (or even had some kind of humor in their response) are well remembered.
Sure there might be people who pirate everything out of principle, but my guess is that the majority will only do it if they can't help it any better.