A voter casts his ballot during a special election in Georgia's 6th Congressional District special election last June. Georgia is the largest state that exclusively still uses electronic voting machines that don't leave a paper trail, a major concern for election officials and cybersecurity experts. Joe Raedle/Getty Images hide caption
Senate Intelligence Committee Chairman Richard Burr, R-N.C. (right), and Ranking Member Mark Warner, D-Va., have released their committee's recommendations to combat cyberattacks. Nicholas Kamm/AFP/Getty Images hide caption
Phil Bredesen, the former Democratic governor of Tennessee, is running for the seat now held by Republican Sen. Bob Corker. Bredesen's campaign contacted the FBI on Thursday about a potential breach of its system. Bloomberg via Getty Images hide caption
The Danaher ELECTronic 1242 voting machine, on display in 2004 at the Franklin County Board of Elections office in Columbus, Ohio. The machines have been in use in the state since 1992. David S. Holloway/Getty Images hide caption
Polling station chairman helps a voter at a voting machine during the Republican presidential primary in February in West Columbia, S.C. Sean Rayford/Getty Images hide caption
Voters stand in line as they prepare to cast their votes in Hialeah, Fla., on Tuesday. Alan Diaz/AP hide caption
A government cybersecurity expert warns against new moves by state election officials to accept online overseas ballots, like those from deployed U.S. troops. Rafiq Maqbool/AP hide caption