There has been a lot of discussion across the Internet over the last several days about the Sony DRM software that installs itself as a rootkit. One of the tools available to see if you have anything like a rootkit installed is Sysinternals RootkitRevealer.
I downloaded it and ran it on my system. It only found two possible problems, and they both were related to the USB driver for my Motorola iDEN i90c cell phone (lets the phone act as a modem). Nothing to worry about for me right now.
RootkitRevealer is probably worth downloaded and running on your system to see what’s going on. Note that the RootkitRevealer web page also has links to several good resources to help you understand what Rootkits are.