China-based hackers are suspected once again of breaking into U.S. government computer networks, and the entire federal workforce could be at risk this time.

The Department of Homeland Security said in a statement that data from the Office of Personnel Management — the human resources department for the federal government — and the Interior Department had been compromised.

"The FBI is conducting an investigation to identify how and why this occurred," the statement Thursday said.

The hackers were believed to be based in China, said Sen. Susan Collins, a Maine Republican.