This has never happened to me since owning a Mac, so I hope to get some help here. I was checking my junk mail account' which is a Yahoo web account, when I noticed non-junk from friends asking why I've been sending them an odd email several days in a row. I immediately ran to my Yahoo account on the computer (Mac Pro) and noticed the emails had been sent to my entire Yahoo web contacts list. I tried deleting the account, but received an error. Since it's a throw-away account, I deleted ALL email messages, trash, spam, sent, etc. I then deleted ALL contacts and changed the account password as well as other web passwords, especially financial ones. I did remember however that after a Snow Leopard disaster months ago, I reformatted my computer. I don't recall reinstalling the Norton antivirus, so I reinstalled it again tonight. That said, most research on this was from a Windows perspective or dated articles. I'd like to know whether this has happened to a MAC user, and what your suggestion would be. Thank you.