Russians were responsible for the recent breach of Arizona's voter registration system, the FBI told state officials in June.
Matt Roberts, a spokesman for Arizona Secretary of State Michele Reagan said on Monday that FBI investigators did not say whether the hackers were working for the Russian government or not, the Washington Post reported. He said hackers gained access after stealing the username and password of an election official in Gila County, rather than compromising the state or county system.
The FBI also uncovered a breach in the voter registration database in Illinois. The hacks added to concerns about security ahead of November's presidential election after other attempts by Russia to meddle in U.S. elections. The Arizona and Illinois findings follow revelations about a Russian hack into the Democratic National Committee computer network in June.
At least two other states are investigating possible breaches, officials told the Post.