winhost.exe is a hijacker which means it will intermittently change your Internet Explorer settings / Desktop to the link of it’s author’s sponsors
I'm not 100% but
Spybot S&D or
Ad Aware should be able to get rid of it if your virus scan hasn't already.
I did a quick search about it and didn't find too much on removal, so I'm guessing semantic and norton can fix it.
-GM