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When our children are admitted to a special or private school, it is likely that our family members, friends etc will come to know about it. Why is this not true with Muggleborn wizards? When Muggleborns go off to an unknown school, and live a secretive life (for example, marrying another wizard), why don't the people around them know about this?
I suppose data on every individual is collected by the authorities of each country. Some of the Muggles know about witches and wizards, and wizards cannot be everywhere all the time to make sure that the Muggles aren't continuously sharing what they know about wizards with the other Muggles.
How do wizards make sure information about the Wizarding World is not revealed by Muggles?