As reported on several news-pages the last days, the author of the rootkit-protection sofware RootkitRevealer
discovered that some Sony Audio CDs install rootkit-like software on your PC.
This is only a very grave case that shows why Digital Rights Management is bad.
The way this and several other copy protected CDs work: You cannot play them with your usual CD-player software on your PC, only if you install some special software delivered on the CD itself.
Beside the fact that you can only use such software if you're using the operating system they write the software for (which is usually Windows) and the fact that you cannot use the audio player of your choice, this leads to a number of other problems.
What this case shows: If you want to play DRM music, you often have to install "something" on your PC you don't know what it really does. You have to trust some unknown software just to play a CD you've bought, and in this case some software that probably leads to security problems, stays on your system without your knowledge and always uses some system ressources.
But think about some other scenarios: You find the CD in let's say 20 years, want to hear it just to find out that nobody uses Windows XP any more, that the software doesn't run on current computers (whatever they'll look like in 20 years). You have no access to the content any more. This is one big issue with DRM-systems: You'll never know how long they'll work.
If you buy a song in iTunes today, you don't know if apple still exists in 20, 30, or even let's say 50 years and if their online-DRM-check finds anything. Same goes with MS/WMA-based DRM-systems. Let's even imagine you want to access some DRM-proted content when the content is no longer copyrighted, you have the right to copy it, but cannot do so.
DRM-systems will have big consequences on the accessibility of older content in the future and that's a big threat to culture at all.
