Put me down in favor of paper ballots.

The FBI warning, contained in a “flash” alert from the FBI’s Cyber Division, a copy of which was obtained by Yahoo News, comes amid heightened concerns among U.S. intelligence officials about the possibility of cyberintrusions, potentially by Russian state-sponsored hackers, aimed at disrupting the November elections.

Those concerns prompted Homeland Security Secretary Jeh Johnson to convene a conference call with state election officials on Aug. 15, in which he offered his department’s help to make state voting systems more secure, including providing federal cyber security experts to scan for vulnerabilities, according to a “readout” of the call released by the department.

Johnson emphasized in the call that Homeland Security was not aware of “specific or credible cybersecurity threats” to the election, officials said. But three days after that call, the FBI Cyber Division issued a potentially more disturbing warning, entitled “Targeting Activity Against State Board of Election Systems.” The alert, labeled as restricted for “NEED TO KNOW recipients,” disclosed that the bureau was investigating cyberintrusions against two state election websites this summer, including one that resulted in the “exfiltration,” or theft, of voter registration data. “It was an eye opener,” one senior law enforcement official said of the bureau’s discovery of the intrusions. “We believe it’s kind of serious, and we’re investigating.”

The bulletin does not identify the states in question, but sources familiar with the document say it refers to the targeting by suspected foreign hackers of voter registration databases in Arizonaand Illinois.