SAN FRANCISCO — The Democratic National Committee said on Wednesday it was alerted to an attempted hack of its voter database this week and has notified law enforcement about the incident.
A cybersecurity researcher from a firm called Lookout contacted the D.N.C. on Tuesday about the attempted intrusion, said two officials briefed on the matter who were not authorized to speak publicly.
The F.B.I. is investigating, according to one of the officials.
A Democratic Party official said the attempted hack targeted the Democratic Party’s voter file, known as Votebuilder. But the efforts, which were described as sophisticated, were not successful, the D.N.C. said.
The two officials said hackers had set up a fake D.N.C. login page that mimicked the political party’s real website, in order to gather the names, passwords and other credentials of those using the voter database. The hackers also sent emails to people within the D.N.C. to try and trick them into using the fake login page, a tactic known as “spearphishing,” the officials said.
“This attempt is further proof that there are constant threats as we head into midterm elections and we must remain vigilant in order to prevent future attacks,” said Bob Lord, chief security officer for the D.N.C.
“While it’s clear that the actors were going after the party’s most sensitive information — the voter file — the D.N.C. was able to prevent a hack by working with the cyber ecosystem to identify it and take steps to stop it,” he said in a statement.
Lookout confirmed that it had been in touch with the D.N.C., and the attempt was also detected by DigitalOcean, a cloud service provider.
Ahead of the midterm elections, political groups and government organizations have been on high alert for hacking attempts and foreign interference.
Earlier this week, Microsoft said it had detected attempts by hackers tied to Russian intelligence, which targeted the Senate and conservative think tanks in the United States, also by creating fake websites of those groups.
Facebook last month also identified a political influence campaign aimed at potentially disrupting the midterms, and this week said it had uncovered other disinformation efforts targeting people around the world.
The D.N.C. was hacked in 2016 during the presidential election campaign, resulting in thousands of confidential emails being released. The emails embarrassed Democratic presidential candidate Hillary Clinton, and may have helped to boost Donald J. Trump as a candidate.
CNN earlier reported the attempted hack of the D.N.C.
Mr. Lord said the White House also needed to get involved. “These threats are serious and that’s why it’s critical that we all work together, but we can’t do this alone,” he said. “We need the administration to take more aggressive steps to protect our voting systems.”