dllhost.exe using 25% CPU - Why?

every so often I notice on my cpu monitor for my quad core that I am using
over 25% cpu at rest. It is normally 0-2%. Task manager shows dllhost.exe to
be stuck at 25% cpu. killing the process gets things back to normal. There
is no evidence of any virus/malware on the system.

I see from google that others are having similar problems but there doesn't
seem to be a slution.

Any ideas?

TIA

Jon