Someone is sending emails to my address book contacts?

To Yahoo, Recently I sent out 50-60 emails from my address book. I was told by all of the senders that each email also included a message (which I did not write or authorize) that included a link. Many of the links were to pharmaceutical companies advertising...

Someone is sending emails advertising their business using our email address and names in our address book. How can I block this from happening? We don't even know it is being done unless someone asks us about the " crazy email we sent them"...

these emails they are sending in my name all contain the words viagra, cialis etc. How do I stop this, people are calling me and asking me to stop sending these emails. I am not sending them.

Some one has gotten into my yahoo address book and is sending all my contacts spam using my email address. What do I do.

I keep getting these messages in my inbox saying mailer domain. I think someone may be sending what they call "bullet mail" through my yahoo account to my contacts to make it look to them like it's a message from me so they will click on it...

Someone has I guess hacked my email and is sending people in my address book junk mail. How can i stop this?

I also changed my password, but I am unsure if contacts will gone prior or after