If you don’t know what multi ID of yahoo messenger is, please be sure you download and used first. You can use multi ID for all Yahoo Messenger, or Multi ID for Yahoo Messenger Version 8. Multi ID sometime calls as Multiple Messenger.
May be you didn’t knew that Multi ID can be used as boot protection or Anti Boot. To find out how Multi ID work as Anti Boot you can read the tutorial below:
Anti Boot With Multi ID
End of Anti Boot Tricks