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A vulnerability found on one of the world’s biggest genetic genealogy websites could leave people’s private data at risk of being accessed without their permission.

At risk are the 1.2 million people who have had a DNA test with other companies and then uploaded their genetic data to GEDmatch, an online database that helps people match segments of their genome with other users to find family members.

Peter Ney and his colleagues at the University of Washington say the service has significant privacy and data issues. The …