WASHINGTON — The suspected hacking attempt of the Democratic National Committee’s voter database was a false alarm, and the unusual activity that raised concern was merely a test, a committee official said on Thursday.
The suspicious phishing activity detected this week had prompted the committee to contact the F.B.I. out of fears that it was another Russian attempt to penetrate the committee, as Moscow did during the 2016 campaign.
The test had similar attributes to an actual hacking, said Bob Lord, the committee’s chief security officer. It was not a test that the committee had authorized, but rather a simulated phishing test built by a third party.
A Democratic Party official who was not authorized to speak about the attack said it was conducted by hackers hired by the Michigan Democratic Party, which did not inform the national committee.
The jolts of panic underscored the continued fear of another major breach of the party’s systems just weeks before the midterm elections, even as computer security has been prioritized and shored up since 2016. American intelligence officials have said there continue to be real threats from Russia to interfere in American elections.
Mr. Lord has referred to the Votebuilder database as “the party’s most sensitive information.”
The database is a particular prize for hackers because it contains personal details on Democratic voters that could be used to unlock other information, including personal email accounts and computer files. Its successful penetration could have set off other hacking in a domino effect, cybersecurity experts said.
“There are constant attempts to hack the D.N.C. and our Democratic infrastructure, and while we are extremely relieved that this wasn’t an attempted intrusion by a foreign adversary, this incident is further proof that we need to continue to be vigilant in light of potential attacks,” Mr. Lord said in a statement.
With the midterm elections just over 70 days from now, political groups and systems administrators have been on high alert.
Microsoft recently detected that hackers tied to Russian intelligence targeted the Senate and conservative think tanks in the United States by creating fake websites. Last month, Facebook discovered a political influence campaign directed at disrupting the upcoming elections. And this week, the social media giant said it had found other disinformation efforts outside the United States.
Yet in this case, the panic was caused from within. The D.N.C., the Democratic Party official said, is more decentralized than the Republican National Committee, allowing states to conduct tests similar to the Michigan one without coordinating with the national party.