I have never encountered this before, and I am a little bit scared. Just this morning, when I signed on to Yahoo! Messenger, a few minutes later, there was a message appear telling me that: "You have been signed out because you signed in on a different computer or device." This is just impossible, right? I never let anyone know my password, and my password is composed of 11 characters, and symbols to form a meaningless word. So how can one get into my account? What should I do now? Should I change my password to a longer one? If suspect there's something not good is lying somewhere on my computer, how can I sweep that fu*king thing out? I used NOD32, but is it good enough? Should I consider Norton Antivirus?