Researchers have shown that it’s possible to link your identity to supposedly secret genetic information about your predisposition to diseases, merely by analyzing family-tree databases and other publicly available information.

“It was quite surprising,” said Yaniv Erlich, a genetic researcher at the Whitehead Institute for Biomedical Research. “When we got the first family, I was surprised. … It’s as if you opened a box that for a long time was locked.”

Erlich led the research team whose work is being published in this week’s issue of the journal Science. The team’s study already has led to a tightening of security measures for federally sponsored genetic databases.

The security-cracking trick relies on the availability of genetic information linked to surnames in a variety of public family-tree databases. DNA samples from males can be tested to look at dozens of genetic markers on the Y-chromosome that change only rarely from generation to generation. If the markers from two individuals with the same surname are a close match, that’s a tip-off that the two are closely related, even if they don’t know each other.