TweakNow RegCleaner 2012
Full user review
"Loads computer with crapware and doesn't work"
Removed about a dozen out-of-date registry entries but not the one causing problems (expired Microsoft installer file.msi security certificate).
Installed smiley crapware, changed default searches and installed Funmoods Toolbar in all three web browsers (Internet Explorer 9, Firefox and Google Chrome). Took me several hours to uninstall them all, clean and restore normal operation.
CNET review from 2008 needs to be updated because the 2012 version of this program is rubbish; seek something better!