The FBI has been investigating a year-long series of successful cyberattack against the campaign of Dr. Hans Keirstead, a Democrat who ran against Rep. Dana Rohrabacher, the Republican incumbent in California who is widely regarded as Russia’s most ardent defender in Congress, Rolling Stone reported Wednesday.

According to emails and forensic documents obtained by Rolling Stone, FBI agents in California and Washington, D.C. devoted considerable resources to investigate the hack, which consisted of a series of attacks on Keirstead’s business email account that he used for the campaign. The hacks began in August 2017 with a phishing email, asking the recipient to share his email password, similar to what hackers did to infiltrate the emails of Hillary Clinton campaign chairman John Podesta.

The FBI did not comment on the Rolling Stone piece and security experts told Rolling Stone it’s impossible to identify the source of the attack without input from law enforcement.

While Keirstead’s campaign told the Rolling Stone that they do not think the attack influenced the outcome of the primary, it is notable that Keirstead lost the election to Harley Rouda — who will face Rohrabacher in November — by just 125 votes.

The Keirstead campaign decided to go public with news of the cyberattack to raise voter awareness that cyberattacks on campaigns large and small is ongoing, as Director of National Intelligence Dan Coats has indicated.

Read the full Rolling Stone report here.