WASHINGTON (AP) — An internal team at the Census Bureau found that basic personal information collected from more than 100 million Americans during the 2010 head count could be reconstructed from obscured data, but with lots of mistakes, a top agency official disclosed Saturday.

The age, gender, location, race and ethnicity for 138 million people were potentially vulnerable. So far, however, only internal hacking teams have discovered such details at possible risk, and no outside groups are known to have grabbed data intended to remain private for 72 years, chief scientist John Abowd told a sc...