Disable sending mail?

Is there a way I can disable my Yahoo! account from sending emails? Today I found out that my account must have been hacked or something, because a few of my friends said they recieved emails from me that advertised for male enhancement drugs. After checking the "Sent" folder, nothing showed up; I'm not sure if they deleted the trails or something weird. I'd like to keep using this account for Answers but I'm afraid something like that may happen again.