A top Microsoft engineer on Friday set out a weekend challenge to the Windows Vista development team: Find and fix a bug in the current code and earn US$100.

The employee who squashed the most bugs before Monday in the US was promised a US$500 prize.

Brian Valentine issued the challenge on Friday in an e-mail to members of the team working on Vista, the next update of the company's Windows operating system.

The move comes as Microsoft is wrapping up work on a broad test version of Vista, expected by many Windows watchers to be released later this month. Microsoft has said it is on track to deliver a test version to roughly two million users this quarter.

Microsoft is pushing to wrap up development of Vista this year, with a mainstream launch slated for January. The company had long hoped to release it this holiday season, but in March announced that the launch would be delayed.

Valentine's e-mail was noted earlier on Friday by Windows enthusiast site ActiveWin.

As bug bounties go, it's small potatoes -- though most others are for outsiders who report flaws. In February, VeriSign's iDefense offered to pay US$10,000 for reports of flaws that end up with a "critical" severity rating in a Microsoft Security Bulletin. And Mozilla offers US$500 and a Mozilla T-shirt to those who find critical security flaws in its products, which include the Firefox Web browser.

CNET News.com's Joris Evers contributed to this report.