May be you don’t know that official yahoo messenger can be used as boot protection or anti boot. Even though, its not always working as good as anti boot or unofficial yahoo messenger such as: YahElite, YmLite, and others, Official Yahoo Messenger Anti boot, is good enough to protect boot attack from small number of bots. For more further explanation how to make anti boot from official yahoo messenger, please, follow this link.
End of Yahoo Anti Boot Tutorial from Official Yahoo Messenger