I've always been curious about this. Now I wouldn't call myself a programmer yet, but I'm learning, so maybe the answer to this is obvious. It just seems a little hard to believe that with all of our technological advances and the billions of dollars spent on engineering the most unbelievable and mind-blowing software, we still have no other means of protecting against piracy then a "serial number/activation key". I'm sure a ton of money, maybe even billions, went into creating Windows 7 or Office and even Snow Leopard, yet I can get it for free in less than 20 minutes. Same for all of Adobe's products, which are probably the easiest.

I guess my question is: can there exist a fool proof and hack proof method of protecting your software against piracy? If not realistically, how about theoretically possible? Or no matter what mechanisms these companies deploy, hackers can always find a way around it?

EDIT: So apparently, the answer is no. There's pretty much no way. And so I'm sure these big companies have realized this as well. Should they adopt another sales model rather than charging a crapload for their software (I know its justified and they put a lot of hard work into their software, but its still a lot of money). Are there any alternative solutions that will benefit both the company and the user (i.e. if you purchase our product, we'll apply $X dollars to your account that will apply to future purchases from our company)?