By ERIC LICHTBLAU and ERIC SCHMITTAUG. 10, 2016
WASHINGTON — A Russian cyberattack that targeted Democratic politicians was bigger than it first appeared and breached the private email 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 F.B.I. 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 email 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 D.N.C. voter analytics program used by Mrs. 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 another batch of 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, Representative Debbie Wasserman Schultz resigned as D.N.C. chairwoman after WikiLeaks released a trove of hacked internal emails showing party officials eager for Mrs. Clinton to win the nomination over Senator Bernie Sanders of Vermont.
American 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 J. Trump.
Mr. Trump stunned Democrats and Republicans when he said last month that he hoped Russian intelligence services had successfully hacked Mrs. Clinton’s email, 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.
F.B.I. officials briefed staff members of House and Senate Intelligence Committees last week on the investigation into the theft of emails and documents from the Democratic National Committee. Briefings for other congressional committees are expected in the coming days.
Much of the briefing to the committee staff focused on the fact that American 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 D.N.C. and the House Democratic committee added a troubling new element to the case, the staff member said.
American 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 emails of lawmakers or staff members who serve on the Intelligence Committees, two staff members said.
The F.B.I. says it has no direct evidence that Mrs. Clinton’s private email server was hacked by the Russians or anyone else. But in June, the F.B.I. 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.
Mrs. Clinton’s aides were concerned about the possibility of an outside breach after a hacker calling himself “Guccifer” got into the email account in 2013 of Sidney Blumenthal, a longtime confidante of Mrs. Clinton’s who often emailed her on her private server, according to new documents released Wednesday.
Cheryl D. Mills, a lawyer and adviser for Mrs. Clinton, said she discussed the 2013 hack with the technician who ran Mrs. Clinton’s private server and considered “whether this event might affect Secretary Clinton’s email,” according to a written account Ms. 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 Mr. Trump, who is known to avoid email, officials said.
Since news of the D.N.C. 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 D.N.C., speaking on condition of anonymity, said the committee took the threat very seriously, but would not comment on specific security steps taken.
WikiLeaks, the group that put out the D.N.C. emails publicly last month, interjected itself into the hacking case again this week when it offered a $20,000 reward for information on the shooting death last month of a former D.N.C. staff member, Seth Rich, outside his Washington home. His killing fueled speculation on the internet that he was somehow tied to the hacked emails, but the police have not given any credence to that speculation.
The WikiLeaks founder, Julian Assange, has made it clear that he would like to hurt Mrs. Clinton’s bid for the White House, opposing her candidacy on policy and personal grounds. He has hinted that he has more material about the presidential campaign that he could release.