(CNN) An attempted hack into a mobile voting app used during the 2018 midterm elections may have been a student's attempt to research security vulnerabilities rather than an attempt to alter any votes, three people familiar with the matter told CNN.

Mike Stuart, the US attorney for the Southern District of West Virginia, revealed at a press conference Tuesday that an FBI investigation "is currently ongoing" after an unsuccessful attempted intrusion into the Voatz app, which West Virginia has used since 2018 to allow overseas and military voters to vote via smartphone. No criminal charges have been filed.

The sources told CNN that the FBI is investigating a person or people who tried to hack the app as a part of a University of Michigan election security course. Michigan is one of the main academic hubs of election security research in the country, housing the trailblazing Michigan Election Security Commission.

The office of West Virginia Secretary of State Mac Warner had previously communicated to Stuart that suspicious activity against the Voatz app came from IP addresses associated with the University of Michigan, one of the people familiar with the matter told CNN.

"During the 2018 election cycle, Secretary of State Warner referred to my office what he perceived to be an attempted intrusion by an outside party into the West Virginia military mobile voting system," Stuart said in prepared remarks Tuesday. He added that "no legal conclusions whatsoever have been made regarding the conduct of the activity or whether any federal laws were violated."

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