Donald Trump on Monday dismissed Hillary Clinton's national security plan by saying it gives away too much information to the enemy, and said that might explain why she's been fighting the Islamic State for her entire life.

Trump made the remark after Clinton encouraged people at the first presidential debate to look at her website, which is serving as a fact checker during the debate. Trump ridiculed that answer and mocked other things on her website, such as her plans to fight the Islamic State.

"You go to her website, and you take a look at her website. She's going to raise taxes $1.3 trillion. And look at her website. You know what, it's no different than this: She's telling us how to fight ISIS. Just go to her website. She tells you how to fight ISIS on her website. I don't think Gen. Douglas MacArthur would like that too much."

"Well, at least I have a plan to ISIS," Clinton said.

"No, no, you're telling the enemy everything you will do," Trump fired back.

"No, we're not," Clinton said.

"You're telling the enemy everything you want to do," Trump said. "No wonder you've been fighting ISIS your entire adult life."

The Islamic State came into existence in 2010 during the second year of Clinton's tenure as secretary of state, and ultimately took over as the top terror group in the Middle East, taking over parts of Syria and becoming a presence all over the region and North Africa.

During the campaign leading up to Monday night's debate, Trump and Clinton have made clear they differ in their approach to defeating the Islamic State and defending the country from the threat of terrorism, while not being as clear in how they differ.

Up to now Trump has described his approach as series of broad ideas, banning immigration from countries where radial Islamism breeds terrorists, instituting extreme vetting, and building a wall along the U.S. Mexico border.

As for how to defeat ISIS faster, Trump has made reference to doing something "extremely tough" and knocking the "the hell out of them."

This month, Trump said he will charge the Pentagon with coming up with a plan within 30 days of when he takes office, and will see if he likes it better than his own ideas. He has famously said he knows more about ISIS than the generals, and is his own best adviser.

Clinton has constantly mocked Trump over the issue, accusing him of claiming to have a secret plan, when "the secret is he has no plan."

Clinton this month called defeat ISIS her "highest counterterrorism goal," and offered a strategy that mirrors the current approach used by President Obama: U.S. and coalition airpower, to enable Syian Arabs, Kurdish Peshmerga and Iraq military forces on the ground, helped by a few thousand U.S. special operations forces and advisers.

Both candidates have called for getting other countries to be involved in the effort, to gather and exploit more intelligence, and to increase cyberwarfare against the terrorist group.

Clinton has ruled out any significant commitment of group troops in Iraq or Syria, though when she pledged during a commander in chief forum this month "We are not putting ground troops into Iraq ever again, and we're not putting ground troops into Syria," Clinton seemed to be willfully overlooking the 5,000 or so U.S. forces there now.

So far neither candidate has offered a plan to end Syria's bloody civil war, where with the help of Russia, the regime of Bashar Assad has turned the tide of battle and now has the upper hand in the battle against rebel fighters, after five years of fighting and an estimated 400,000 civilian deaths.