I've found my software as cracked download on Internet, what to do?

This is obvious a highly personal reaction. I don't expect anyone else to share it: Celebrate! Someone thinks your software's worth stealing!

• (a) It's impossible to prevent people from stealing your software,
• (b) trying to only irritates your honest customers and
• (c) people stealing your software means that you have solved the single biggest problem: obscurity. If no one knows of your program, no one's buying it. At least if someone's taken the trouble to crack your software, people know about your product. Another answer here offered several interesting ways of getting people to pay for your product.

This reminds me of the autodesk/kinetix response, tho they claimed that the response was a complete accident, a byproduct of the crack itself.

A cracked version of 3DSMax had a nasty side behavior - each time it opened a model file it corrupted the vertex coordinates just a little bit more- not enough to be noticable on any given run, but over time, a lot of damage could take place. The cost of the program might be thousands, but the cost in time and dollars to repair the damage dwarfed that.

The mfgr claimed this was a complete accident/side effect of the crack, and to their credit here, I believe repaired something in their software - that said, they certainly delivered a powerful message to their user base......

Don't get the wrong idea - I'm not recommending this, especially since IANAL - on the other hand, I've always found it's an interesting anecdote

open source your software, then you won't have this problem :-)

Also consider price. I have no idea what your software is but there are multiple markets for every product. For example Photoshop has a normal version that is a little out of the cost range of anyone wanting to touchup their vacation shots. For this reason they make elements, it doesn't do as much but it does serve a market. If your software is expensive and of limited personal use try releasing a home version. A trial version, an ad supported version.

What every you don't attempt to detect hacked versions. This type of DRM only annoys real users

i think that developing your programs considering a sponsor will protect your rights (espacially financial ones ) remarkably.

You'll never make your application crack-proof, but some copy protection is better than others. For instance, whatever the copy protection on Cubase is, it's hell to get through. It was cracked eventually obviously, but after much much more effort. Might be worth a shot.