It's said that since I began using Windows 7, in the Beta build 7000 back in January 2009. Using Avast. I don't think it's anything to worry about. The system is aware you have a AV installed. You can tell from the action center giving you a popup when you don't have one installed. Had discussions of it from a long time ago, can't remember exactly what the answer was for why it's like that though. Either something with the programs vendor not bothering registering some file with it for detection in the health report, or having to be on Windows 7 fault that they never bothered fixing yet.