As it turns out, no one accessed my account. However, Yahoo indicated the problem arose from someone being able to replicate the address from one of those annoying chain emails someone put me on. I never participate in these and don't even open them. I don't care if it is joke related, religious related, or has "IMPORTANT: Must Read, Could Save Your Life" indicated in the subject.
Now, I can get on with the good stuff and begin to show you all the new stuff I'm working on! Can hardly wait!