Question how do we keep sites from scanning our PCs to see if we have an ad blocker installed? what can be done if anything to stop them from doing that. If they can scan for an ad blocker im guessing they are scanning for everything we have installed.
They do not scan your computer. Their scripts running in your browser just check for a cookie or a session parameter that should have been set by the ad-showing script. If that's missing, you have an ad blocker.
Any program which runs right is obsolete.