Yahoo trojan or virus or something else?

The window below pops up several times an hour. The one time that I entered a password a spam email was immediately sent to all of my friends. I ran a program called ClamXav but that didn't help. How can I determine where this is on my system and remove it?

I didn't see your image - looks like I have to sign up for it.

I think your Yahoo email account has been hijacked. This has nothing to do with your Mac. Yahoo mail is a webmail service (I think - I don't use yahoo mail) - so your addressbook is there on Yahoo.

You should either - close the Yahoo account and get a new one, or, change the Yahoo password to a long, secure one.

Image

I'll try again to include the image. I just really want this box asking for my yahoo email password to stop popping up all the time. After the initial spam email went out, I changed my email password and haven't had any more spam issues, but this pop up won't leave me alone.