What was released, and what was not new
As part of implementing a proposed surcharge on homes that are not the owner's primary residence, New York's Department of Finance published assessment data covering properties that may fall under the new category, with owners' names listed alongside the addresses. The city describes the release as routine and legally required, part of a long tradition of public assessment records that let owners inspect and contest their tax treatment. The file also sweeps broadly: reporting indicates it lists far more properties than will ultimately owe anything, which means many people appear on it who will never be touched by the tax itself.
Property records have been public for a century. Anyone with time and intent could always assemble a picture of who owns what. What changed here is not disclosure but aggregation: a single, cleaned, categorized file that pairs identity with a wealth signal and a residential address, released to everyone at once. That distinction, between data that is technically public and data that is packaged for retrieval, is the entire security story.