Running Windows 7 on my laptop, I had this same problem and worked on fixing it for 5 days. I would get 4 or 5 instances of dllhost.exe files in my system folder and the CPU useage went from 10% to almost 100%. I deleted the ones with the higher size but they would just come back. The computer would lag and I just couldn't do anything. Finally I found the culprit. I also kept getting a pop-up Windows message saying "Powershell has stopped working". The problem was a Poweliks Trojan virus which was residing in the System32 folder. You can't see it if you look in the folder or find it by searching.
There is an application called ESET Poweliks Cleaner that I downloaded and used to find the file and it also deleted it. It has been 2 days and I have had absolutely no more problems. The multiple instances of the dllhost.exe file have not returned and computer is running normal with low CPU useage.
I hope this helps you and everyone else solve this issue.