An investor lawsuit against Yahoo Inc's board over its rebuff of Microsoft Corp's $47.5 billion buyout bid was made public by a judge on Monday who said that Yahoo had not shown good reason to keep it confidential.

A copy of the unsealed complaint, and a letter from Delaware Chancery Court Judge William Chandler explaining his decision, were posted on the Web site of law firm Bernstein Litowitz Berger & Grossmann LLP, which represents investors in the case.

"I conclude that defendants have not satisfied their burden to show good cause for the continued filing of the portions of the complaint under seal," the judge wrote.