[artur]

I think a solution would be to make the registration check only once a month and if the account does not exist, lock up the whole application. This way people could use it off-line when needed and plug it in on first of each month to re-activate it.

This would be much better than constant connections to your server. I know piracy is a big deal, but poor piracy preventions only discourage your potential clients to actually buy your product. If this is how you want it, I encourage you to rethink the issue. This is not how you end up with big bucks.