FBI Director James Comey said Wednesday hackers have attempted to infiltrate voter registration sites in more than a dozen states, and officials suspect Russia is behind the intrusions.

Comey told the House Judiciary Committee the FBI has detected an unspecified number of “scanning activities, a potential intrusion activities as well as some attempted intrusions at voter database registrations beyond those we knew about in July and August,” CNN reported.

During the summer it had been reported hackers attempted to break into the voter registration databases in Arizona and Illinois.

There are concerns the hacking represents an effort by Russia to create distrust in the U.S. election process. Republican nominee Donald Trump repeatedly has said if he doesn’t win, it means the Nov. 8 election “is going to be rigged.”

"We are urging the states just to make sure that their deadbolts are thrown and their locks are on and to get the best information they can from [the Department of Homeland Security] just to make sure their systems are secure," Comey said. "Because there's no doubt that some bad actors have been poking around."

Homeland Security Secretary Jeh Johnson said Tuesday 18 states have asked for cyberassistance to help protect their voting systems.

Rigging the U.S. election would be difficult. There are 180,000 voting districts and no centralized system for counting the vote. Voting systems aren’t even connected to the internet or to each other.

“The truth is, the voting process is the most secure it’s ever been,” Tom Hicks of the Election Assistance Commission told Time magazine.

voter registration Darlene Pedrosa, 54, (right) registers to vote on National Voter Registration Day at the Los Angeles County Registrar-Recorder/County Clerk's office in Norwalk, Sept. 27, 2016. Photo: Lucy Nicholson/Reuters

“We know there is some fraud in the U.S. system, but it has always been in the margins,” Jason Healy, a senior research scholar at Columbia University in New York City and a former White House director of Critical Infrastructure Protection, told Mashable.

The Democratic National Committee was hacked during the summer, and the hackers, suspected to be Russian, released emails indicating the DNC favored Hillary Clinton over Bernie Sanders.

Steve Morgan, founder of the cyber security research firm CyberSecurity Ventures, told Mashable rather than messing with the vote count itself, hackers could use information from the voter registration systems to send emails warning of violence at the polls to keep turnout down or could hack systems that manage voter rolls, shutting down operations if there’s no paper backup.