The FBI has arrested a California man who they believe is responsible for hacking the campaign website of one of former Rep. Katie Hill Katherine (Katie) Lauren HillObama counsels NBA players on forming a social justice committee Republicans cast Trump as best choice for women House GOP campaign chairman insists party will win back majority MORE's (D-Calif.) Democratic rivals leading up to the 2018 primary.

Arthur Dam, whose wife Kelsey O’Hara was Hill’s fundraiser during the campaign and later her district director, is accused of coordinating cyberattacks against Bryan Caforio, one of Hill's Democratic rivals.

Dam's arrest and the criminal complaint against him was first reported by The Intercept.

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According to Federal Election Commission filings, Dam provided “graphic design and website security consultations” for Hill's campaign for $500.

Hill, who eventually flipped the California congressional seat, resigned from Congress late last year after nude images of her were leaked online and a House Ethics Committee investigation was launched into allegations that she had an inappropriate relationship with a staffer.

Caforio, who was supported by the progressive group Justice Democrats, and another primary contender, Jess Phoenix, both had their websites hacked leading up to the election, but Hill did not. The FBI launched a probe shortly after her election in 2018.

The criminal affidavit states that Caforio's website was targeted by four distributed denial-of-service (DDoS) attacks between April 2018 and May 2018, forcing it offline for a total of 21 hours. One of the attacks happened shortly before a live primary debate, forcing it offline throughout the debate, the complaint stated. The final attack happened about a week before the primary election.

"In May 2019, the Victim provided information to the FBI that as a result of the DDoS attacks, the Victim suffered various harms, including a reduction in political donations and campaign visibility, and between approximately $27,000 and $30,000 in expenditures and lost time to respond to, investigate, and mitigate the attacks," the complaint filed Wednesday reads.

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Hill, who has yet to address Dam’s arrest, eventually won the California primary by fewer than 3,000 votes.

“I’m absolutely shocked and saddened to learn today that Katie Hill’s campaign associates hacked my campaign in order to help her advance through the primary,” Caforio told the Intercept. “This should serve as a reminder that Russia is not the only threat to our democracy. There are bad actors on all sides who will do anything for their own personal gain, and we need to come together as Americans to defend our country and hold everyone responsible accountable.”

The Hill has reached out to a lawyer for the former congresswoman for comment.