Mark Russinovich: A few weeks ago my wife complained that her Vista desktop was not responding to her typing or mouse clicks. Given the importance of the customer, I immediately sat down at the system to troubleshoot. It wasn�t completely hung, but extremely sluggish. For example, the mouse moved and when I clicked on the start button the start menu opened after about 30 seconds. I suspected that something was hogging the CPU and likely could have resolved the problem simply by logging off or rebooting, but knew that if I didn�t determine the root cause and address it, she�d likely be calling on my technical support services again in the near future. In any case, stooping to that kind of troubleshooting hack is beneath my dignity. I therefore set out to investigate.

My first step was to run Process Explorer to see which process was using the CPU. After a few minutes Process Explorer finally appeared and showed that not one, but two processes were involved, each consuming 50% of the CPU: Iexplore.exe and Dllhost.exe. Iexplore is Internet Explorer (IE) and I suspected that IE itself wasn�t the problem, but that it was a browser helper object (BHO), ActiveX control, or some other plugin loaded into IE. Similarly, Dllhost.exe is the host process for out-of-process COM server DLLs, so it was probably not at fault, but the COM server loaded into it. Both required digging deeper and I decided to tackle IE first.