DRM is installed on your computer whenever you install a new release game on it. (with exceptions, valve, stardock, etc)
iTunes is packed full of DRM. The problem isn't the DRM itself (although it seems to generate less sales rather than reduce piracy), but with rootkits that are installed along with it in some cases. (this was the case with sony, starforce, and the recent discussions about spore, for examples)
They aren't viruses, but they're definitely not welcome.