...mail on cialis and viagra.? I don't give my password to anyone ever. I use avg anti-virus and ensure it is up to date. From time to time I clear my internet cache.
Have you checked your 'sent' folder and is the email in there? I once received an email 'from myself' but there was nothing in my sent folder so technically they hadn't hacked into my account. They found a way of opening an account with an identical email address as mine. Same thing happened to my boss and he isn't with yahoo it's the company name! Not sure how they do it though.
Most likely what happened is someone spoofed your address rather than actually accessed your account. This happens all the time. It's basically the same as how they get your email address to send you spam. Usually it's just a scrip that cycles through a number of possible combinations.