WASHINGTON — A Russian cyberattack that targeted Democratic politicians was bigger than it first appeared and breached the private e-mail accounts of more than 100 party officials and groups, officials with knowledge of the case said Wednesday.
The widening scope of the attack has prompted the FBI to broaden its investigation, and agents have begun notifying a long list of Democratic officials that the Russians may have breached their personal accounts.
The main targets appear to have been the personal e-mail accounts of Hillary Clinton's campaign officials and party operatives, along with a number of party organizations.
Officials have acknowledged that the Russian hackers gained access to the Democratic Congressional Campaign Committee, which is the fund-raising arm for House Democrats, and to the Democratic National Committee, including a DNC voter analytics program used by Clinton's presidential campaign.
But the hack now appears to have extended well beyond those groups, and organizations like the Democratic Governors Association may also have been affected, according to Democrats involved in the investigation.
Democrats say they are bracing for the possibility that more damaging or embarrassing internal material could become public before the November presidential election.
The attack has already proved politically damaging. On the eve of the Democratic National Convention in Philadelphia last month, Florida Representative Debbie Wasserman Schultz resigned as DNC chairwoman after WikiLeaks released a trove of hacked internal e-mails showing party officials eager for Clinton to win the nomination over Senator Bernie Sanders of Vermont.
US intelligence agencies have said they have "high confidence" that the attack was the work of Russian intelligence agencies. It has injected a heavy dose of international intrigue into an already chaotic presidential campaign as Democrats have alleged that the Russians are trying to help tilt the election toward the Republican nominee, Donald Trump.
Trump stunned Democrats and Republicans when he said last month that he hoped Russian intelligence services had successfully hacked Clinton’s e-mail, and encouraged them to publish whatever they may have stolen, although he said later that he was being sarcastic.
Intelligence and law enforcement officials, however, are taking the issue seriously.
FBI officials briefed staff members of House and Senate intelligence committees last week on the investigation into the theft of e-mails and documents from the Democratic National Committee. Briefings for other congressional committees are expected soon.
Much of the briefing to the committee staff focused on the fact that US intelligence agencies have virtually no doubt that the Russian government was behind the theft, according to one staff member, who spoke on condition of anonymity to discuss elements of the confidential briefing.
The extension of the hack's scope beyond the DNC and the House Democratic committee added a troubling new element to the case, the staff member said.
US authorities remain uncertain whether the electronic break-in to the committee’s computer systems was intended as fairly routine cyberespionage or as part of an effort to manipulate the presidential election.
Russian motives are still an open question, said a federal law enforcement official, who also spoke on condition of anonymity.
There is no evidence so far that the theft penetrated the e-mails of lawmakers or staff members who serve on the intelligence committees, two staff members said.
The FBI says it has no direct evidence that Clinton's private e-mail server was hacked by the Russians or anyone else. But in June, FBI Director James B. Comey said that intruders had tried, and that any successful intruders were probably far too skilled to leave evidence of their intrusion behind. Law enforcement officials said he had the Russians in mind.
Clinton’s aides were concerned about the possibility of an outside breach after a hacker calling himself “Guccifer” got into the e-mail account in 2013 of Sidney Blumenthal, a longtime confidant of Clinton’s who often e-mailed her on her private server, according to new documents released Wednesday.
Cheryl D. Mills, a lawyer and adviser for Clinton, said she discussed the 2013 hack with the technician who ran Clinton's private server and considered "whether this event might affect Secretary Clinton's e-mail," according to a written account Mills provided to Judicial Watch, a conservative legal group that is suing the State Department.
So far, it does not appear that the Russian hackers sought or gained access to any computer systems used by Trump, who is known to avoid e-mail, officials said.
Since news of the DNC hack broke in June, a number of Democratic organizations have been scrubbing their files to determine what internal information might have been compromised. They have also been shoring up their cybersecurity defenses to guard against another attack.
An official with the DNC, speaking on condition of anonymity, said the committee took the threat very seriously, but would not comment on specific security steps taken.