The federal government on Friday told election officials in 21 states that hackers targeted their systems before last year's presidential election.

The notification came roughly a year after U.S. Department of Homeland Security officials first said states were targeted by hacking efforts possibly connected to Russia. The states that told The Associated Press they had been targeted included some key political battlegrounds, such as Florida, Ohio, Pennsylvania, Virginia and Wisconsin.

The AP contacted every state election office to determine which ones had been informed that their election syste...