Voter registration databases and other election systems in two states have been hacked, according to the FBI and local officials, who launched an investigation this month following the discovery of malicious software on a state computer.

In an Aug. 18 warning notice obtained by Yahoo News, the FBI said that hackers penetrated two state election databases in recent weeks. The warning lists several suspicious IP addresses and claims that hackers used "penetration testing" software, including Acunetix, SQLMap, and DirBuster, in an attempt to gain access to election systems.

"The FBI is requesting that states contact their Board of Elections and determine if any similar activity to their logs, both inbound and outbound, has been detected," the warning notice said. "Attempts should not be made to touch or ping the IP addresses directly."

Although the warning did not specify which states were targeted, Yahoo and local news reports identified Illinois and Arizona. In Arizona, officials cooperating with the FBI shut down part of the state elections website that displays information on campaign financing. Officials also identified a compromised login credential that was used to access a computer connected to the state's voter registration system, according to Arizona Central.

In Illinois, officials shut down the voter registration system for 10 days in late July after hackers managed to download personal data on up to 200,000 state voters, a state board of elections official told Yahoo News.

The FBI did not identify the source of the suspicious login attempts. In a separate investigation, the agency is looking into reports of Russian hackers targeting the Democratic National Committee and the campaign of presidential hopeful Hillary Clinton. Yahoo News reports that that one of the IP addresses listed in the FBI alert has surfaced before in Russian criminal underground hacker forums.