Identification of anonymous DNA using genealogical triangulation

Consumer genetics databases hold dense genotypes of millions of people, and the number is growing quickly. In 2018, law enforcement agencies began using such databases to identify anonymous DNA via long-range familial searches. We show that this technique is far more powerful if combined with a database of the type collected by online ancestry services. We present a genealogical triangulation algorithm and study its effectiveness on simulated datasets. We show that for over 50% of targets, their anonymous DNA can be identified (matched to the correct individual or same-sex sibling) when the genetic database includes just 1% of the population. We also show the effectiveness of snowball in which a successful identification adds to the genetic database, increasing the identification accuracy for future instances. We discuss our technique9s potential to enhance law enforcement capabilities as well as its privacy risks.