Upon receiving a security message in Club Pogo that an application had an expired security certificate, I mistakenly checked the box that said, "Always trust certificates from this publisher". Now I'd like to change this selection and "un-trust" the application's publisher. I'm running Windows XP Professional Service Pack 3. My decision seems to affect both Mozilla Firefox 3.6 and Internet Explorer 8, so there must be a file of "trusted publishers" somewhere in Windows, but I don't know how to undo my original decision.