The hell is the moonlight MPEG 2 viewer

A few days ago I started to see a stupid logo dancing on the video player screen when I play some video. I finally got feed up and checked it out online. Turned out that it was caused by a Moonlight MPEG2 codec luring for money (activate some player by playing some shit money). This is crazy since I never installed this moonlight player. Finally I had to go to the damn Moonlight site to download an uninstaller (DecCleaner.zip). And then I don't see that crap logo anymore. But damn I am still pissed. To me it sort of behaves like a spyware (having something installed without my consensus.