Shell Hardware Detection is disabled, autorun/autoplay turned off. And still the pop-up comes when I attach an external hard disk.
By the way, it has nothing to do with a browser, only with Windows 7. I hope that there will be still something else that can be done, except performing the scan. I know from experience that such a scan can mess up data I don't want to risk to loose. And when the external disk works without problems, the scan is really unnecessary.