A Homeland Security Department official says hackers have targeted the voter registration systems of more than 20 states in recent months.
The official was not authorized to speak publicly on the subject and spoke on condition of anonymity.
The FBI last month warned state officials to improve their election security after hackers targeted systems in Illinois and Arizona.
FBI Director James Comey told lawmakers this week that the agency is looking "very, very hard" at Russian hackers who may try to disrupt the U.S. election.
U.S. officials say the decentralized nature of election systems, which are run by state and local governments, and the fact that they're generally not connected to the internet, makes it hard for hackers to alter the election outcome.
© 2016 The Associated Press. All rights reserved.
