The census contains some data that commercial databases are legally prohibited from holding (e.g., info about children within a household). The deanonymization

The census contains some data that commercial databases are legally prohibited from holding (e.g., info about children within a household). The deanonymization/reidentification attacks rely on joining census data against commercial datasets to produce something beyond what either contains. It's not accurate to say this information is already semi-public, because a good deal of it is not.