I'm just curious. What if someone were to crack a program to get past a registration window/process and then bring this vulnerability to light? Can the owner/creator prosecute you for doing so, even if you were trying to help him or her?
I am not a lawyer. Basing your actions on anything I've written will be at your own risk. If searching for legal advice you should really consult an expert in the relevant legal field instead of community-driven sites
First of all, cracking a program is not the same as finding a vulnerability in it. Although cracking a program may cause financial damages to the manufacturer, it does not pose any risk to the users. Additionally, except for unique DRM-ed software and where advanced anti-theft features are in place, manufacturers do not tend to combat cracks too thoroughly, piracy is an accepted lost of revenue to some extent.
I'll start by pointing at a relevant Israeli proverb - Peeing from the diving stand:
The statement is based on the fact that everyone knows that many pee in the swimming pool. While the general public prefers to ignore this wrongful act that it can not act against, the public will not stand in silence if someone does the same thing, peeing in the pool, from the diving stand.
This goes to say if you're doing something wrongful, which you're aware might have legal implications, you should at least do it in private and not boast about it.
Now, for the legality of cracking a piece of software and reporting that to the manufacturer; Although this greatly depends on the laws in the country / state you live in, it is usually not illegal per say but does violate most End User License Agreements, which you're bound to by using the software. Most software EULAs explicitly forbid any type of reverse engineering of the provided software and any of it's components.