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The Department of Homeland Security will audit election equipment, purchased by a firm targeted by Russian hackers, in North Carolina after voter registration malfunctions led to long lines in Durham County in 2016.

The investigation will seek to put to rest one of the lingering questions from the contentious 2016 election: why electronic poll books in Durham County, which allow poll workers to check in registered voters on Election Day, mistakenly showed many voters as having already voted. That forced an emergency move to paper pollbooks, creating long lines to vote.

“This support may help to provide a better understanding of previous issues and help to secure the 2020 election,” DHS spokeswoman Sara Sendek told CNN. News of the investigation was first reported by The Washington Post.

After the 2016 election, Durham County hired a local cybersecurity firm, Protus3, to conduct an audit of what went wrong. It concluded that the issues were due to a series of human errors, and not due to outside forces or the fault of the Florida-based pollbook manufacturer, VR Systems.

But the combination of equipment failure that led to long lines in a purple state, alongside the Russian interference campaign of 2016, has raised percolating concerns that something more nefarious had happened in Durham county. Details of the Russian campaign that have been unearthed since the election suggest that Russians particularly targeted county officials who used VR Systems, which provided the machines in Durham, and that they successfully breached two Florida counties.

VR Systems has long maintained that Russia never hacked its primary network. In a statement to CNN, COO Ben Martin said that “we welcome the DHS review of Durham County elections systems” adding he was “confident” the audit would prove the company’s software wasn’t compromised.

For some officials at the time, the Protus3 audit was sufficient.

“I’m aware of no basis whatsoever to conclude there was any kind of tampering with the equipment or anything else,” Bill Brian, the Durham County Board of Elections Chair in 2016, told CNN.

“I don’t know of any reason why there would need to be a federal investigation of what happened in in Durham County in 2016, unless the federal government just plain doesn’t have enough to do,” he said.

Protus3’s report, a redacted version of which was acquired by CNN, shows that the company made significant backups of 13 laptops used in the election. The state election board also has images of the machines, as well as the machines themselves.

DHS policy is to not proactively search local government computers, but to offer such services as an option if local officials make the request. In May, North Carolina’s Democrat-majority Board of Elections ousted longtime executive director Kim Strach and replaced her with Democrat Karen Brinson Bell.

“We appreciate the Department of Homeland Security’s willingness to make this a priority so the lingering questions from 2016 can be addressed in advance of 2020,” Brinson Bell said in a statement.