A Microsoft computer security expert who advocated for a key feature of the Windows Vista operating system -- billed as the company's most secure -- is leaving for Amazon.com.

Jesper Johansson, senior security strategist in the security technology unit at Microsoft, gave notice on his blog Friday evening after circulating an internal e-mail. The news comes as Microsoft heads to the Black Hat security conference in Las Vegas this week.

Johansson is credited with advocating for the least-privileged user account configuration, which limits access rights to maintain security and will be the default setting in Windows Vista. eWeek has more on this.

He also co-authored "Protecting Your Windows Network", a top security book.

Johansson said on his blog he leaves Microsoft Sept. 1 and starts at Amazon on Sept. 5 as principal security program manager.