Is it scvhost.dll or svchost.dll ? if the former there is a nasty inhabiting your computer.
My advice would be firstly to download a couple of spyware removal programs & then also run an online virus scan. Please do the following.
Download & instal Adaware from here
& update it B4 scanning.
In settings under 'scanning,' have it set to
'scan within archives,'
'scan active processes,'
'scan my IE Favourites for banned URL's,'
'scan my host's file.'
In 'tweaks' under 'scanning engine' set it to 'unload recognised processes during scanning.'
Also in 'tweaks' under 'cleaning engine' set it to 'Automatically try to unregister objects prior to deletion' & 'let Windows remove files in use at next reboot.'
Select 'activate in-depth scan' before starting scan.
When the scan is finished select 'next.'
Remove what it finds by placing a check in the box to the left of the object. Reboot
Download & instal Spybot S&D from here Update it B4 scanning. Go into settings & have it check for Beta releases also & download if available.
After the scan is complete, have spybot fix everything marked RED.
On the page that first opens when you start Spybot there is an option to immunise, you should do this. In the immunise section there is also a link to download Spywareblaster. Download that & you can keep it updated by selecting the same link that you use to download it. Reboot
Go here for an on-line scan & set it to autoclean for you.
If the problem persists then also do the following.
Download HijackThis from here & unzip it into it's own, permanent folder, (not a temporary folder & not on the desktop). Start HJT & press the scan button. When the scan is finished the scan button will change to save. Save the log to a text file, copy the entire contents of the text file & paste it into the body of your post. DO NOT FIX ANYTHING YET. Most of what is there is harmless & even necessary to the running of your system.