What is this ? in my taskbar,i saw a invisible icon known as mIRC 32,when i click "exit",it start again and pop up a advertisment web. i can't search any spyware or virus from it. WHY ?

definately a spyware drone which idles in botnet waiting for command

yea, true. sugest you stop the thing with ctrl-alt-del. Kill the process. But if the problem is still there, try updating us with the info. good luck.