If I were a security researcher and put a lot of effort into finding vulnerabilities for Yahoo I would have simply sold the exploits to the highest bidder, and invited Yahoo to participate in the auction. If they lost, then I'd go to the press with the story of how little their user's security means to them (again to the highest bidder.) Either way, (only in the long run in the second case), the users win and I'd sleep like a baby.
It's just as well I'm not a security researcher.
Edit: Wow a lot of drive-by-downvotes. I'm not serious guys, but I hope I have made some people think about the moral issues involved. It's not as clear as people are making it out to be in other comments on this post.