A computer system used by Hillary Clinton's presidential campaign was hacked, a spokesman for the Democratic nominee said Friday.
Nick Merrill said in a statement that the cyber breach was part of a larger hack attack on the Democratic National Committee (DNC) that was made public earlier this week.
The violation concerned a DNC analytics data program used by the Clinton campaign and "a number of other entities," Merrill said. He added that security experts hired by the campaign had found "no evidence" that the campaign's own internal systems were compromised.
However, such third-party, connected systems represent appealing options for hackers searching for less-protected routes to attack an organization.
Soruces familiar with the incident confirmed to Fox News that the FBI is investigating the breach as well as another cyberattack on the Democratic Congressional Campaign Committee (DCCC).
The investigation was first reported by Reuters, which said that the Justice Department's national security division was investigating whether the cyberattacks threatened the U.S.
An FBI statement did not mention the Clinton campaign specifically, but said it was aware of reporting "on cyber intrusions involving multiple political entities, and is working to determine the accuracy, nature and scope of these matters."
It is not clear what types of data the DNC service was analyzing, but partnerships with modern e-commerce companies can allow sophisticated tracking, categorization and identification of website visitors. This can help organizations tailor their online content, advertising and solicitations to be more effective.
The report that Clinton's campaign was hacked comes the same day that the cyberattack on the DCCC, which raises money for Democratic congressional candidates, was made public. Sources told Fox News Friday that the DCCC hack bears similarities to the breach of DNC files.
President Barack Obama has said Russia was almost certainly responsible for the DNC hack, an assertion with which cybersecurity experts have agreed.
Two private cybersecurity firms have said they found evidence pointing to Russian government involvement in the DNC hack when they analyzed the hackers' methods and efforts to distribute the stolen emails and other files. The hacker groups, identified as Cozy Bear and Fancy Bear, used different but sophisticated techniques to break into the DNC and try to avoid detection. Most of the DNC emails appeared to have been stolen May 25.
The DNC breach led to the leak of 19,000 internal emails by WikiLeaks that appeared to show a pro-Clinton bias in the organization -- and, in turn, led to DNC Chairwoman Debbie Wasserman Schultz stepping down ahead of this week's Democratic National Convention.
The hack of the DCCC’s web server allowed the hackers to create and redirect traffic to a fake donations page, made to look and feel authentic, sources said. From there, hackers were able to capture all data entered on the page. Sources said the objective behind the hack is not clear, though it could be to harvest data on Democratic donors and supporters.
Additionally, Fox News has obtained analysis of the DCCC hack from private sector cybersecurity firm FireEye that suggests the intrusion was carried out by a Russian-government aligned hacking group dubbed "Tsar Team (APT28)."
In its research, FireEye notes it previously confirmed that malware analyzed from the DNC hack was also consistent with "Tsar Team", which has been implicated by FireEye in numerous cyberattacks aimed at foreign targets on behalf of the Russian government in the past.
Computer hacking, emails and indications of Russian involvement have evolved into a political issue in the presidential campaign between Clinton and Republican candidate Donald Trump.
This week, Trump encouraged Russia to seek and release more than 30,000 other missing emails deleted by Clinton, the former secretary of state. Democrats accused him of trying to get a foreign adversary to conduct espionage that could affect this November's elections, but Trump later said he was merely being sarcastic.
Clinton deleted the emails from her private server, saying they were private, before handing other messages over to the State Department. The Justice Department declined to prosecute Clinton over her email practices, though FBI Director James Comey called her "extremely careless" in handling classified information.
Fox News' Matt Dean, Serafin Gomez and the Associated Press contributed to this report.