Yahoo's shares momentarily soared by 10% when current CEO Jerry Yang announced he was stepping down.

But now they've come right back down again on the news from Microsoft that it's not going to buy the ailing web company.

As he has done before, Microsoft chief Steve Ballmer laid it on the line: "Let me be as clear as I think I've tried to be publicly. We are done with all acquisition discussions with Yahoo", he told Microsoft's annual shareholders meeting, in response to a question on what was happening with Yahoo.

"I've said that a bunch of times. Somehow some people have gotten confused nonetheless. We thought we had something that made sense. (It) didn't make sense to them. We've moved on."

Yahoo's shares fell 19% following Ballmer's comments.

However, Ballmer did hint that Microsoft could be interested in a web search partnership.

"There's no active discussion on that front. But we'd be very open to it. But acquisition discussions are finished", he said.