The Obama administration says hackers stole Social Security numbers from more than 21 million people and took other sensitive information when government computer systems were compromised.
The Office of Personnel Management says more than 19 million who had applied for background investigations were affected. The government also said nearly 2 million people were also affected who weren't applicants, but rather their spouses or other family members.
The number affected by the breach is higher than the 14 million figure that investigators gave The Associated Press last month. They said the government was increasingly confident that China's government, and not criminal hackers, was responsible for the extraordinary theft of personal information.
China has publicly denied involvement in the break-in.