Windows 7: block unsolicited contact on yahoo mail/messenger?

with the new version of yahoo mail we keep getting messages from prostitutes and sex workers thanks to Yahoo and its family values corporate strategy. Is there any way to disable ALL messenger functions and just keep the mail function? we have not installed yahoo messenger as a stand alone program, it is forced when you have yahoo mail. went to their options - privacy and selected "block messages from persons not in your contact list" and clicked ok but we still get unsolicited messengers. Grrrr. wonder how much money Yahoo makes promoting these people. Thanks

Msongs