Prof. Felton explains why CD DRM leads to spyware:

So if you’re designing a CD DRM system based on active protection, you face two main technical problems:

1. You have to get your software installed, even though the user doesn’t want it.
2. Once your software is installed, you have to keep it from being uninstalled, even though the user wants it gone.

These are the same two technical problems that spyware designers face.