U.S.: More than 21 million affected by government data breach

WASHINGTON -- Hackers stole Social Security numbers, health histories and other highly sensitive data from more than 21 million people, the Obama administration said Thursday, acknowledging the breach of U.S. government computer systems was far more severe than previously disclosed.

The scope of the data breach -- believed to be the biggest in U.S. history -- has grown dramatically since the government first disclosed earlier this year hackers had gotten into the Office of Personnel Management's personnel database and stolen records for about 4.2 million people.

Since then, the Obama administration has acknowledged a second, related breach of the systems housing private data individuals submit during background investigations to obtain security clearances. That second attack affected more than 19 million people who applied for clearances, as well as nearly 2 million others, the administration said.