WASHINGTON — Hackers targeted voter registration systems in Illinois and Arizona, and the FBI alerted Arizona officials in June that Russian hackers were behind the assault on the election system in that state.
The bureau told Arizona officials that the threat was "credible" and severe, ranking as "an eight on a scale of one to 10," said Matt Roberts, a spokesman for the Secretary of State's Office.
As a result, Secretary of State Michele Reagan shut down the state voter registration system for almost a week in June.
It turned out that the hackers did not succeed in compromising the state system or even any county system, but rather had managed to steal the user name and password for one Gila County elections official.
The revelation comes amid news that the FBI is investigating suspected foreign hacks of state election computer systems, and this month warned states to be on the alert for intrusions.
In Illinois, officials discovered an intrusion into their state voter registration system in July.
The FBI's Aug. 18 warning follows heightened concern over Russian hacks of Democratic Party organizations and possible meddling in the presidential election.
Although the hackers did not alter any data, the intrusion into the Illinois database marks the first successful compromise of a state election database, federal officials said.
Until now, countries such as Russia and China have shown little interest in voting systems in the United States. But experts said that if a foreign government gains the ability to tamper with voter data, for instance by deleting registration records, such a hack could cast doubt on the legitimacy of U.S. elections.
Meanwhile, the recently discovered hacks have state officials across the country scrambling to ensure that their systems have not been compromised. At least two other states are looking into potential breaches, officials said. The two states were not named.
"This was a highly sophisticated attack most likely from a foreign (international) entity," said Kyle Thomas, director of voting and registration systems for the Illinois State Board of Elections, in a message that was sent to all election authorities in the state.
In July, officials in that state discovered the intrusion, in which hackers were able to retrieve voter records. The amount accessed was "a fairly small percentage of the total," said Ken Menzel, general counsel for the Illinois elections board.
State officials alerted the FBI, he said. The Department of Homeland Security also got involved, he said. The intrusion led the state election board to shut down the voter registration system for a week.