Actually I find windows(7) quite secure - most flaws are from third party software - Adobe - Flash - Java etc..
I will not call it secure until windows core/source become really solid and un-touchable like you feel every file or program you run is being opened in a sandbox, when you uninstall a program no leftover remain or no kind of input being able change anything from windows core. (Emmm, like a Chrome Extension which cannot change the way whole browser works, or like a JAVA mobile OS which applications cannot change the way mobile OS works)