In the 80s when viruses first started to raise their ugly little heads Microsoft made an unfortunate and, in hind sight, foolish decision. They decided to let third parties deal with the problem and concentrated on other things. The likely reason was that viruses weren't seen as a product defect they were intentional attacks on the product by third parties. However, much like automobile companies had to step up to Auto theft problems by installing door locks, security systems, and even connected services like On Star, Microsoft should have stepped up to this problem but didn't.
The end result was an Anti-Virus security industry that was motivated to break into Microsoft's offerings in order to provide solutions that would fix what was broken. This basically started an arms race not only between the security firms and the virus writers but between Microsoft and both the virus writers and the security firms. This was a race that lowered significantly the perceived value of Microsoft's offerings and went a long way towards damaging Windows customer satisfaction and the perception of product quality.
Plugging the Hole
Early this decade Microsoft realized they had a problem but realized that if they now built in the much needed Anti Virus capability they would have anti-trust problems both in the US and the EU even though they were actually responding to a real product threat. It is with some irony that the Anti-Virus security firms had help drive a condition where Microsoft was forced to try to eliminate the Anti-Virus market for Windows in order to assure Windows quality and the safety of Windows users.
The EU, which has been more aggressive in terms of anti-trust behavior, has already taken the position that Microsoft should provide products that create a barrier to entry for third party offering (like media players) as a download service and not as part of the OS. Since Anti Virus solutions have to be updated constantly putting one in Windows wasn't really practical anyway and this provided Microsoft with a way to both plug this ugly hole and avoid an Anti-Trust exposure.
As a result they are supplying One Care for free and using it as a tool to both improve the security of all legal copies of Windows and increase the customer satisfaction with the Windows product platform. The end result should be a vastly better product experience because Microsoft can assure their Anti Virus product doesn't create problems with software updates and that beta products work with it. Both of these will also improve the overall perception of Windows.
Cautionary Tale for Apple
This isn't being done to compete with Apple but it does point to a similar problem that Apple is ignoring at the moment and that is that Apple doesn't really own security on their product either and viruses, botnets, and other malware can be put on Apple products as well. Apple probably should follow Microsoft's lead and own security for their platform as well or the Anti Virus vendors are likely to see them as the low hanging fruit now that Windows is moving to be largely unavailable to them as a platform.
Wrapping Up
In the current economy free is an excellent price and a big reason for why botnets are so prevalent is that too many people don't run good, up to date, Anti Malware products. That is about to change and this will shift focus from Windows as the target of these attacks to Apple and Linux, in fact many argue Linux is already the favorite platform for Bots Masters because it exists on products that aren't touched often and that don't typically run antivirus solutions.
This move by Microsoft may, in hindsight, be the biggest strike against malware writers and Bots Masters, and it should have come years ago.



