The FBI is investigating a series of cyber attacks that targeted Californian Democrat Dr. Hans Keirstead, though the identity of the hackers is still being investigated, the attacks did occur to the Democratic frontrunner challenging GOP U.S. Rep. Dana Rohrabacher, often referred to as “Putin’s favorite Congressman.”

“There was a very sophisticated and very highly coordinated attack on both my campaign digital services, but also my company,” said Keirstead on Thursday. “They went for the duration of my campaign, and both of them stopped when I lost the primary.”

Keirstead, who hired two cybersecurity firms — one for his campaign and another for his company, both of which were targeted — said that neither firm was able to identify the source of the hacks.

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However, Keirstead offered his own theory, the source of the fishing attempts could be Russia, due to the fact that the hacks concluded following his loss in the primary. Though he does not believe that the attempts affected the outcome of the race, and he quickly threw his support behind Harley Rouda, another Democrat, after losing by just 125 votes.

Rohrabacher, a strong supporter of President Donald Trump and Russian interests in Congress, was warned in 2012 by the FBI that Russian spies may be trying to recruit him.

In 2017, Rohrabacher told ABC News, “they call me Putin’s best friend. I’m not Putin’s best friend. I’m a patriotic American who knows that it would be really good for America to cooperate with Russia. I could care less whether it’s good for Russia.”