How to manually edit the search providers in Windows Internet Explorer 9

On a Windows 7 system, the search provider has been hijacked, and keeps prompting us to change it when Internet Explorer 9 starts up. It brings up the Manage Add ons dialogue, and we can click on any of the providers, but clicking Set as Default does nothing. We can delete anything other than the one that is ironically named nothing, and it even does it if I launch Internet Properties without IE9 starting. I then tried to Reset all the settings, but it did not change anything.

Where in the registry or on the filesystem does Windows store this data so I can manually remove the entries?

Answer

For user-specific search providers, edit this registry key:

HKCU\Software\Microsoft\Internet Explorer\SearchScopes

For system-wide search providers, edit this registry key:

HKLM\Software\Microsoft\Internet Explorer\SearchScopes