Russia's intrusion involved numerous methods... This was a big one:
Intrusions into state voter-registration systems- During the summer and fall of 2016, Russian hackers intruded into voter databases and software systems in 39 different states, alarming Obama administration officials to the point that they took the unprecedented step of contacting Moscow directly via the Moscow-Washington hotline and warning that the attacks risked setting off a broader conflict. Obviously, this was inadequate but that is another discussion.
As early as June 2016, the FBI sent a warning to states about
"bad actors" probing state-elections systems to seek vulnerabilities. In September of 2016, FBI Director James Comey testified before the House Judiciary Committee that the FBI was investigating Russian hackers attempting to disrupt the 2016 election and that federal investigators had detected hacker-related activities in state voter-registration databases, which independent assessments determined were soft targets for hackers. Comey stated there were multiple attempts to hack voter database registrations. Director of National Intelligence James Clapper attributed these Russian hacking attempts to Vladimir Putin.
In August 2016, the FBI issued a nationwide "
flash alert" warning state election officials about hacking attempts. In September 2016, U.S. Department of Homeland Security officials and the National Association of Secretaries of State announced that hackers had penetrated or sought to penetrate, the voter-registration systems in more than 20 states over the previous few months. Federal investigators attributed these attempts to Russian government-sponsored hackers, and specifically to Russian intelligence agencies. Four of the intrusions into voter registration databases were successful, including intrusions into the Illinois and Arizona databases. Although the hackers did not appear to change or manipulate data. Illinois officials said that information on up to 200,000 registered voters was stolen. The FBI and DHS increased their election-security coordination efforts with state officials as a result of this breach.
All of this information is readily available on the internet with a simple Google search of
"Russian interference in the 2016 United States elections".