If you’re having problems with dllhost.exe consuming a lot of resources, along with problems viewing folders in windows explorer it may not be caused by malware. The quick explanation is that it could be related to a corrupt media file, with a decent probability that file is on your Desktop. The screenshot below shows some of the problems I was having with windows explorer; thumbnails wouldn’t show up and the sidebar wouldn’t populate.
The problems extended a bit further, I’d have to manually refresh after renaming files and at times explorer would constantly try loading folders. These problems occured constantly even right after a fresh reboot. They all showed up shorty after performing one of my least favorite tasks on a computer, video conversion. Apparently one of dllhost’s responsibilities is initiating thumbnail generation and if you happen to have a corrupt media file on your computer it’s possible for dllhost to malfunction. This manifests itself as large processor and memory usage, and poor windows explorer performance.
If this is a constant problem, it’s likely the suspect file is on your desktop, or somewhere out in the open. This is because dllhost has to parse your file in order to hang, if it’s occurring right at start-up the problem is probably caused by windows attempting to render the icons on your desktop. I was able to successfully track down the file using a program called Proccess Monitor available from microsoft here: http://technet.microsoft.com/en-us/sysinternals/bb896645.aspx
Set the filter to include the process name “DllHost.Exe” this will filter out any unnecessary process data. With proccess monitor listing for data kill the dllhost.exe proccess from the task manager. It should restart automatically and populate process monitor with data. If your lucky scrolling to the bottom of the output will have a file listed multiple times. In my case, this was the file that was causing all of the problems.
My problem was a .wmv file from a failed conversion. In order to delete the file I had to kill the dllhost process again. It’s a bit tricky as it instantly tries to process the file again after you kill it. If you’ve sent the file to the recycle bin you’ll likely encounter further trouble as explorer will hang when you open the recycle bin, preventing you from emptying the recycle bin. This can be worked around by right clicking the bin on the desktop and emptying from the context menu.