Often spyware comes bundled with free software, like games. If you remove the spyware, the game will no longer work. Other products come with language buried in the EULA stating that you must accept spyware, even from third parties, and allow them access to your computer 24/7 and not attempt to remove it except through their methods (which are designed to leave the problem in your computer). Some are so nasty that they won't even allow you to discuss or rate the product, no matter how crappy it is.
That is why it pays to be careful about downloading free software. Some you can trust. But games, you have to be wary about it because you pay either with money or with ads. Unlike ads on this forum, you cannot stop the ads from those games. And, if you disable the spyware, your game no longer works.
Even worse than this adware is spyware that tracks your movements. Some have keystroke loggers. These programs are out to steal your personal data so they can pull other, worse crimes. That kind of spyware is often put in your computer without your even knowing it's there.
As I see it, botware is the worst. This is a virus that rigs your computer to send spam and commit other cybercrimes. The person who is operating the botware is the one that gains the money. Your computer is the one that physically plants the viruses and writes and sends the spam, but you are not in control of it. The operator typically hijacks thousands of computers in what's known as a botnet. And you can get into trouble if you find your computer is on a botnet, since it will be you and not the operator that gets traced back to. That is what makes botware so much worse than regular viruses and spyware, which are bad enough. At least a regular spyware will not make you into a suspect.
