Hillary Clinton’s campaign network was breached by hackers targeting several large Democratic organizations, Reuters reports.

Clinton’s campaign spokesperson Nick Merrill confirmed the hack in a statement. “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. Our campaign computer system has been under review by outside security experts. To date, they have found no evidence that our internal systems have been compromised,” he said.

The hack follows on the heels of breaches at the Democratic National Committee and at the Democratic Congressional Campaign Committee earlier this year. More than 19,000 emails from DNC officials were published on WikiLeaks just prior to the Democratic National Convention, casting a shadow over the proceedings.

Some security experts and U.S. officials have attributed the breaches to Russian operatives, although the origin of the email leak is less certain.

The DCCC is working with CrowdStrike to investigate the breach, according to Reuters. CrowdStrike also investigated the earlier breach at the DNC.

The FBI said in a statement to the New York Times that it is aware of media reports of the breach and is “working to determine the accuracy, nature and scope of these matters.”

“The cyberthreat environment continues to evolve as cyberactors target all sectors and their data,” the FBI added. “The FBI takes seriously any allegations of intrusions, and we will continue to hold accountable those who pose a threat in cyberspace.”