Protecting your code, and an authentication method.

Hey guys,

I have been working on this project for some time now and have made a really useful tool for people to use. I want to sell my software (1 month, 3 month, lifetime licenses, etc). I have two worries.

• Someone will reverse engineer my program and take the source code which I worked hard on.
  
  
• People find a way to bypass my user authentication system.

So my question here, for those more experienced in the subject, is...

• What is the best and most sure way to protect my code? (I don't want hackers unwinding it)
  
  
• What is the best and most sure way to set this user authentication system up?

I ask about the protecting source code part because with previous programs I have made and shared for free. I have had other people de-compile my "protected/encrypted" .exe file and send me the code...

For the user authentication part, I was thinking of making an online database, mySQL or something along those lines. But the problem with that is that I will probably have to input the database details into the source code... which again brings me back to worry #1. If the source code can be unraveled, then my entire database becomes a security hazard.

Any ideas and/or suggestions will be GREATLY appreciated!