As news surfaced of a potential hack into campaign computers, a campaign spokesman issued a statement late today saying, "An analytics data program maintained by the DNC, and used by our campaign and a number of other entities, was accessed as part of the DNC hack."
The campaign's computer system "has been under review by outside cyber security experts," and so far "they have found no evidence that our internal systems have been compromised," the spokesman said.
The Clinton campaign shares some of its proprietary information -- such as voter data -- with the DNC, and that information was compromised, a campaign official told ABC News.
A campaign aide said that the hackers had access to the analytics program server for about five days. The system, used to conduct voter analysis, does not include Social Security numbers or credit card numbers.
"Anytime there is hacking like that and release of proprietary information, it is a crime," CIA Director John Brennan said today of the DNC hack. "Who is responsible for what happened there, I think, is to be determined."
Nevertheless, government sources privately suspect Russian hackers are behind the cyber attacks on Democratic organizations.
Speaking at the annual Aspen Security Forum in Aspen, Colorado, Brennan vowed that when the U.S. intelligence and law enforcement community determines who is behind it, "there will be discussions at the highest levels of the government" over how to respond.
"Obviously interference in the U.S. election process is a very, very serious matter, and I think certainly this government [would] treat it with great seriousness," Brennan added.
Brennan said the nation will now have to look at "what the vulnerabilities are to the [election] system out there," and while some locations may ultimately decide to go with paper ballots, the country should focus on strengthening the security of the relevant cyber systems.
Meanwhile, the FBI today said it "takes seriously any allegations of intrusions, and we will continue to hold accountable those who pose a threat in cyberspace."
"The FBI is aware of media reporting on cyber intrusions involving multiple political entities, and is working to determine the accuracy, nature and scope of these matters," the FBI said in a statement. "The cyber threat environment continues to evolve as cyber actors target all sectors and their data."
Not only did the hack into DNC apparently allow the cyber operatives to steal opposition research on Republican nominee Donald Trump, but many suspect it led to the theft of internal messages that show efforts by DNC officials to undermine Democratic candidate Bernie Sanders during the primary season. Those damaging emails have since been released by WikiLeaks, agitating Sanders supporters ahead of the Democratic convention in Philadelphia.
Director of National Intelligence James Clapper said yesterday he's "taken aback a bit by ... the hyperventilation over" the hack of the DNC, adding in a sarcastic tone, "I'm shocked somebody did some hacking. That’s never happened before."
The American people "just need to accept" that cyber threats and computer-based attacks are a major long-term challenge facing the United States, he said. Clapper added that Americans should "not be quite so excitable when we have yet another instance of it."
Additional reporting by Cecilia Vega.