Well, it's a start. Microsoft is openly challenging hackers and security professionals to
crack Vista. Unfortunately, this is only a publicity stunt. I say this for two reasons: time and closed source.
Time is a big problem. It's not likely that hackers can find serious flaws at the conference. Sure some flaws could be found, and promptly fixed, but the window of opportunity is too small. Serious flaws are usually found only after lengthy investigations. Its a matter of gathering enough information to make an informed attack.
Which ties closely to my point about closed source. If security professionals cannot examine the source code then they cannot adequately test Vista's security. If Microsoft really wants to make Vista secure, they should provide as much information as possible to the hackers. This will allow them to make informed attacks immediately, while at the conference.
Microsoft, of course, won't make this information available. It goes against many common-sense, but wrong, approaches to security. After the conference, I'm sure Microsoft will be touting how well Vista did against the hackers. Like I said, it's a publicity stunt.
I don't doubt that Microsoft is trying to make Vista secure. They've had so much bad publicity over recent years that security has to be a priority for them now. But being the #1 operating system in the world also means you are the #1 target. Microsoft needs to engage the security community more effectively if they are truly serious about improving Vista's security.