"I think I read that," Trump said. "And I heard it, and somebody--"
"Where?" Holt pressed him.
"—that also gave me that information. I will report back to you," Trump said.
U.S. officials have told NBC News that there is no evidence that hackers penetrated the server, although there is evidence of phishing attempts. Clinton's campaign says that there is no evidence that her private server was ever hacked.
Trump's remark comes a day after he argued that Clinton's private server left her vulnerable to blackmail if she were president.
"Her server was easily hacked by foreign governments -- perhaps even by her financial backers in Communist China -- putting all of America in danger," Trump said Wednesday in a speech that slammed Clinton. "Then there are the 33,000 emails she deleted. While we may not know what is in those deleted emails, our enemies probably do. So they probably now have a blackmail file over someone who wants to be president of the United States. This fact alone disqualifies her from the presidency."
NBC News fact-checked some of Trump's claims in the speech.
Trump's campaign offered alleged examples of attempted hacks from China and other countries in a published version of his Wednesday address, but none of the cited reports say that Clinton's server was ever successfully penetrated as the candidate argued.