We just knew that by using Yahoo Messenger 10 there is one important bug that can be used to make someone disconnected from Yahoo Messenger. We found this tricks while we go to one of biggest Yahoo Messenger forum (you should know about it). This would be important to be resolved / fixed soon by yahoo. Here are the tricks:

Just put this code to your Yahoo Messenger Status Message (We tested in Version 10)

ymsgr:-kill View My Webcam

You can also change the View My Webcam text into something else. Whenever someone click your Status Message link, it would make him/her disconnected in a second (very fast indeed): Yahoo Messenger Crash / Shutdown Automatically.

Another Status Message that would make someone who clicked disconnect:

ymsgr:call?&&&&&&& / or add a name

ymsgr:getplugin?&type=4&id=jammer&name=&&&&&&&&&&

ymsgr:chat?&&&&&&&&

Remember this bug only appears in Yahoo Messenger 

(even some users said that sometimes it also works with YM Ver 9).

Source