I just found this, which is helpful:
http://support.microsoft.com/kb/930367
"Jesper" wrote:
> Not sure if my previous response made it. The web client has been flaky.
>
> > I have a program that, according to Logitech, is now Vista "compliant." I
> > uninstalled the old version. Rebooted and didn't get a "Blocked" program
> > balloon. I reinstalled (the new compliant version) and rebooted and the
> > "Blocked" balloon is back, except this time when you click on it to see the
> > offending software, it lists Setpoint twice.
>
> I'd call Logitech if I were you. It sounds as if their installer is not
> removing things properly.
>
> That said, the popup you are getting sounds like it is from Windows
> Defender. If you click it it should bring up Defender with an option to
> permit the program. Sorry, but I don't have a machine handy with a blocked
> program so I can't tell you exactly what form it will take. It may be a
> right-click option, but I think it is just a permit button. If you permit the
> program to run the warning should go away and everything should work properly.
>
> > I understand that this is how UAC is supposed to work
>
> Unless I am totally misunderstanding the form of these popups, this is not
> UAC you are seeing. It is almost certainly Windows Defender.