Windows security is built on layers of compatibility which makes the OS slow and consumes more resources (RAM, CPU, etc.). This is the price of trying to be compatibile with everything you can toss in a PC over the past 30 years. The compatibility layers are huge security holes and is the reason why Windows 7 (and Vista and XP) have 5-10 security updates every week of every year the OS implemented Windows Update services.
If Microsoft want to move forward and be able to financially keep up with Apple, they NEED to start from a fresh OS slate and toss compatibility out the window. Ground up build of an OS is LONG LONG LONG overdue at Microsoft. If people need to live in the past and retain compatibility with their existing games/applications, then Dual Boot and VM (Virtual Machine) have been around a long time and work VERY well. This is the lesson Microsoft seem unwilling or unable to learn ... it maybe too late given Google's fresh slate OS due out soon.
It's sad to see what Ballmer has done to Microsoft, his lack of vision has left them behind Apple financially and a huge Giant like Goolge is about to release a new secure OS on the world and what is Microsoft trying to do ... come up with Tablet OS to take on iPad. Shakes head, Ballmer just doesn't get it.
Ballmer rode the "leverage" wave for a long time, now that the wave has finally hit the shore he's got nothing.