This is why I switched to Gmail. Yahoo mail is simply not trustworthy. I had to rush to find all my old Yahoo passwords to quickly get my Yahoo accounts back under my control. I don't use them any more, but there's no way I'm going to allow someone else to hijack them.
The CEO should be fired for allowing this disaster to happen in the first place.
On top of that, Yahoo deletes your mail if it get to a certain age. This is simply unacceptable. Gmail never deletes my mails, no matter how old. So what if I have mails 7 years old. My mail provider is NOT allowed to delete them without my permission. Doing so will force me to jump ship.