What is the YahooID of the account you are having trouble with?
What Yahoo properties have you used in the last month?
(e.g. Yahoo Mail, Yahoo Messenger, Yahoo Answers, Yahoo Groups, Yahoo Search, Yahoo Finance, etc.)
When did you last log-in to Yahoo?
Where are you located (city/state or city/country)?
Have you recently accessed the internet from any other locations?
What virus scanning software do you use and when did you last run a virus scan?
Do you have any reason to believe that anyone else may have gained access to Yahoo account, and if so, by what means?