FlexibleResponse,
There is no secret data that comes up when you passport is read. When it goes into the machine all that comes up is what is on you bio-details page.
If you are wanted by any of the border agenices (usually only either Customs or Immigration) then the officer will be alerted to that fact and you wil be escorted off accordingly. At that point in time the offical does not actually know why you have been stopped. While there maybe info on you, it does not present any details when the passport is read.
Also there is almost no info shared between countries, as amongst other things none of the border agencies across the world have integrated computer systems.
Unless you have a very colourful history with the law at your destination, all they will know is what the airline is required to send them which is your flight travel movements and boi-details that the airline gets off your passport at checkin.
Times will change and every country is different but I can assure you there is 'no secret data', And highly doubt there is any truth to the CX story. You can write in and request what they know about you.