What was the Massachusetts Governor (William Weld) re-identification, and why is it historically important?

In 1997 Latanya Sweeney re-identified Governor William Weld in "anonymous" medical records by linking them to public voter data using birth date, sex, and postal code.

Massachusetts released supposedly anonymous state-employee hospital records for research. Researcher Latanya Sweeney bought the public voter registration roll for Cambridge and matched it to the medical data on just three quasi-identifiers — birth date, sex, and ZIP/postal code. Governor Weld lived in Cambridge; only a handful of people shared his birthdate there, and only he was his sex among them. She reportedly mailed his own health records to his office.

Historical importance: it was a landmark public proof that removing names (pseudonymization) alone cannot protect privacy — quasi-identifiers re-link people. It directly motivated k-anonymity and the modern field.

Tip: This is the origin story of the "87% from ZIP+DOB+gender" statistic — and of taking quasi-identifiers seriously.

Go deeper:

• Latanya Sweeney (Wikipedia) — the researcher who ran the Weld attack and produced the 87% statistic.