There are some people who are calling this a brilliant move while others are saying it is stupid and dangerous. No matter what you call it, the one thing for sure is that this is a different way to test.
During the past few years Microsoft has received a lot of criticism because of the security flaws in their operating system. It seems as if there was a constant stream of new ones being discovered. Microsoft wants to try to find ways to reduce the flaws and criticism.
About 3,000 people attended the Black Hat security conference. Microsoft challenged them to break Vista's security. They will be trying to do it with a beta version of the new operating system.
The general belief is that some flaws are going to be found. But this will give Microsoft a chance to fix them before it is released and therefore end up releasing a product with a lot less flaws.
One view of this is that if flaws are found Microsoft can say it was a beta and a beta can't expected to be perfect. At the same time they will have eliminated many of these bugs before release and saved themselves some embarrassment. After all, some of the best computer experts in the world will be looking for the flaws and will take pride in finding them.
This could also be some very good public relations work on the part of Microsoft because this surely could give the impression that they are very serious about security.
Here is a link to an article that has more information about this
Network Security - Microsoft Dares Hackers To Test Vista