After some big cases of companies using rootkit-like techniques without letting the users being aware of it, the problem of protecting users against this kind of threats revealed itself in its huge complexity. This is why an officer of the Department of Homeland Security suggested that putting outlaw rootkits could be a solution.

Now, apart from the proposal of the Department of Homeland Security, what comes immediately to mind is that companies thinking of using root-kit like techniques for protecting their own intellectual property should not do so for a simple set of reasons (mostly good sense):

they make users' computers vulnerable to attacks as soon as the rootkit-like software is discovered (remember Breplibot?).
there will be surely somebody finding your rootkit-like software: a security researcher, a hacker or maybe just somebody who downloaded some rootkit scanner and just gives it a try. It is completely unrealistic to think of the whole computer user base as completely untrained and unable to reason.
the possible economical loss if the attempt is discovered is much greater than what you gain by using such DRM techniques.
the image of the company could be seriously compromised.
you risk to harm only the legitimate user of your product: referring to some famous case related to music CDs, probably the only ones who installed the player (and thus the rootkit-like software) were persons that bought the CD and just wanted to play it on the PC. Others would just download the mp3s from P2P networks.

It is for the above silly reasons (and probably more I can't think of now) and not just for the fear of the law that companies should not using rootkit-like techniques...

http://reversingitout.blogspot.com/2006/02/outlaw-rootkits.html