When it comes right down to it, most Linux users will agree that the security issue is one of the primary reasons we prefer it over Windows. Microsoft and Bill in particular know they have to compete (or at least seem to compete) with their competitor's strengths. FUD saying that they were already more secure wasn't working, so now they strive to make people believe they will become more secure (without of course admitting to not being secure enough in the first place).

I have to say this statement was a long time in coming. We'll see how effective they actually are.