LAS VEGAS - After suffering embarrassing security exploits for several years, Microsoft is trying a new tactic: inviting some of the world's best-known computer experts to try to poke holes in Vista, the next generation of its Windows operating system.

Microsoft made a test version of Vista available to about 3,000 security professionals at the Black Hat security conference as it detailed the steps it has taken to fortify the product against attacks that can compromise bank account numbers and other sensitive information.