Hillary Clinton staunchly defended her use of a private email server during Wednesday’s debate – but made some questionable claims about what was allowed.

Defending her use of a private email server, now the subject of an FBI investigation into whether it was improperly used for classified information, the former secretary of state said: "It was not prohibited. It was not in any way disallowed. ... I did not send or receive any emails marked classified at the time.”

Here are the facts:

Clinton is correct that when she began using the private email system in 2009, federal law did not explicitly prohibit doing so.

But her own department warned its employees against the use of private email to conduct government business because it could compromise classified materials and be subject to hacking.

Clinton herself signed a cable in 2011 sent to diplomatic and consular posts advising that State Department employees should “avoid conducting official Department business from your personal e-mail accounts.”

The latest headlines on the 2016 elections from the biggest name in politics. See Latest Coverage →

Clinton further claims she didn’t need permission to use private email because former Secretaries of State Colin Powell and Condoleezza Rice did so. However, neither Powell nor Rice conducted all government business on personal email, and neither set up a separate, personal server for that purpose.

Meanwhile, while Clinton says nothing was marked classified at the time, the 2009 Non-Disclosure Agreement (NDA) she signed in her early days as secretary of state confirmed that markings don’t matter.

The NDA says classified information is marked and unmarked and includes verbal communications – leaving the responsibility to her to recognize classified information and report when it is outside secure channels.

And while Clinton maintained the emails were retroactively classified, sworn declarations from the CIA to the intelligence community inspector general say information included in the emails from the CIA was classified when it hit the Clinton server. 

Clinton discussed the emails at Wednesday's Univision debate in Florida. She made similar comments during a Fox News-hosted town hall in Detroit on Monday. 

In the year since Clinton turned over 55,000 pages of emails to the State Department, the agency has since censored hundreds of those emails because they contained classified materials.

And when Clinton agreed last March to turn over "all" of her emails to the State Department and urged their release, she acted only after her aides had combed through all of her private emails, withholding messages that they deemed to be personal.

Those decisions weren't made by federal records specialists who normally decide which materials need to be turned over.

Fox News’ Catherine Herridge and The Associated Press contributed to this report.