The FBI is warning state officials to boost their election security in light of evidence that hackers targeted related data systems in two states.

In a confidential "flash" alert from its cyber division, first reported by Yahoo News and posted online by others, the FBI said it's investigating the pair of incidents and advised states to scan their systems for specific signs of hacking.

The FBI didn't name the states that were targeted, but it described a "compromise" of one elections board website and "attempted intrusion activities" in another state's system. State election websites in Illinois and Arizona experienced hack-related shutdowns earlier this summer. In both cases, the parts of the websites affected involved online voter registration.

Yesterday, California's Secretary of State website was down for several hours, but the office says there is no evidence the outage was the result of an intentional hack.

Today, FBI Director James Comey says the FBI puts a high priority on thwarting any hacking effort that might influence U.S. elections. What could this mean for the future of electronic voting? How else could bad actors manipulate voter information, apart from actual ballots?

With files from the Associated Press.

Guests:

Cory Bennett, editor of POLITICO Pro Cybersecurity; he co-wrote the recent article, “FBI alert sparks fears that state voting systems are under digital assault”

David Dill, professor of computer science at Stanford University and founder of VerifiedVoting.org, a voting resource organization whose mission is 'Safeguarding Elections in the Digital Age'