The FBI has arrested a California man linked to the 2018 campaign of former Rep. Katie Hill, D-Calif., and accused him of carrying out cyberattacks on the website of one of her Democratic primary rivals.

In a criminal complaint filed Wednesday, FBI Special Agent Elliot Weideman accused Arthur Jan Dam of "intentionally damaging and attempting to damage a protected computer." He also claimed Dam was involved in four cyberattacks that disrupted the website of one of Hill's primary opponents.

Dam's arrest was first reported by The Intercept.

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The complaint did not name the candidate whose website was targeted by the attacks in the spring of 2018. However, identifying information in the document indicates the victim was Bryan Caforio, who lost to Hill by fewer than 3,000 votes in the so-called "jungle primary" in California's 25th District.

“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 website reported that Hill's Federal Election Commission records include a $500 in-kind donation from Dam for "graphic design and website security consultation."

The complaint also found Dam to “be connected to the cyber-attacks through subscriber information, IP addresses, geolocation history, and open sources, including through his employer and his wife, K.O., who worked for one of the Victim’s opponents." Dam’s wife, Kelsey O’Hara, was Hill’s fundraiser during the campaign and later served as her district director after she won the seat.

"The Victim reported suffering losses, including website downtime, a reduction in campaign donations, and time spent by campaign staff and others conducting critical incident response," the complaint said.

The complaint stated that the four Distributed Denial of Service (DDoS) attacks, one of which occurred just before a debate involving Hill, Caforio and fellow Democrat Jess Phoenix, knocked the rival candidate's website offline for a total of 21 hours. It does not say whether Hill or O'Hara had any knowledge of the attacks.

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"I have no information or knowledge about any of the conduct alleged," Hill said in a statement to USA Today. "These charges do not reflect in any way on the thousands of honest, hard-working staff, volunteers and supporters who worked on my campaign, to whom I owe so much.

Hill resigned from office in October amid a House Ethics Committee investigation following allegations of an affair between her and her legislative director, as well as reports that she was in a so-called “throuple” relationship with husband Kenny Heslep and a campaign staffer.

A special election for the 25th congressional district is set for March 3.

Fox News' Talia Kaplan contributed to this report