Margie is getting a ton of suggestions from autocomplete when she starts entering an email address in Yahoo mail. She can hover the mouse over the unwanted contacts and hit the X to delete them, but that could be a herculean endeavor. Sounds like Yahoo has screwed up the address book. Leo says it's not going to get better and he suggests shifting to Gmail. She can even set Gmail to get her Yahoo Mail and forward it.
The chatroom says that if she looks in her sent folder in Yahoo, she may find emails being sent that she didn't know about. That would indicate that her mail was compromised and has been used to send spam.