Someone is sending spam to people in my yahoo address book from my yahoo mail.?

Your account got compromised. First change your password. Account help.a href="http://help.yahoo.com/l/us/yahoo/acct/in…"http://help.yahoo.com/l/us/yahoo/acct/in…/a for just about anything to do with your account. Then run anti Virus and Anti Spyware. Should be fine then.