A US district court judge Friday blocked a settlement proposal between Microsoft and plaintiffs represented in over 100 private antitrust class-action lawsuits that have been consolidated under his jurisdiction.

District court judge J Frederick Motz wrote in his 21-page opinion that he was not convinced the deal would have produced a fair conclusion to the case. The proposal would have funnelled about $1 billion worth of computers, software and support to the nation's poorest schools.

Motz wrote: "I can not presently determine the adequacy of the proposed settlement, because the record has not been sufficiently developed on the question of the underlying value of the class claims."

Microsoft expressed disappointment in the decision, but said it was "confident" that it would ultimately prevail in the litigation. Tom Burt, deputy general counsel for Microsoft, said: "Microsoft is always open to looking for reasonable ways to resolve litigation. We will review the courts opinion, and at the same time move forward with the next steps in the litigation."

Dan Small, an attorney with Cohen, Milstein, Hausfeld & Toll PLLC, who represents individual and corporate plaintiffs in the case, said: "We're disappointed, of course, that the settlement did not receive preliminary approval. We believe it would have done a lot of good. We certainly respect the court's decision, and we are prepared now to litigate the case against Microsoft."