A rash of recent high-profile cyber attacks has security experts scrambling to find solutions.

“You cannot have an unrealistic set of expectations and believe your system will never be penetrated,” Michael Chertoff, former Secretary of Homeland Security under George W. Bush, told Yahoo Finance at the annual Concordia Summit in New York City. “You need layers of defense so your systems have resiliency.”

Chertoff, who now runs his own risk management company, stressed that cyber security involves much more than code. Among other things, he says companies must be armed with backup systems to store data in case their servers are compromised. In the video above, Chertoff compares a company’s cyber security system to the human body.

“We take a holistic approach,” he explained. “The human body doesn’t keep all bacteria and viruses out, but it also has an immune system and that’s what companies should have.”

He added that companies shouldn’t get in the business of paying off hackers. “It’s a mistake to pay because you’ll wind up paying again and again.”

Accept more refugees

Chertoff also spoke about the need for the United States to accept more refugees.

“A common-sense strategy from a national security standpoint says we ought to be taking in a reasonable amount, higher than the [current] 50,000.”

Chertoff added that having a low cap puts our allies who are hosting these refugees in a difficult position.

“We’re asking them to assume the burden of the refugees, but we’re not willing to partner with them,” Chertoff said. “If you turn the refugees away, you risk them becoming victims or worse, getting recruited by terrorists.”

Chertoff noted that not letting in more refugees could also put our military at risk.

“I remember when we were in Iraq and I was Homeland Security Secretary, many people applied to be refugees because their families had worked with US forces as translators, as guides, doing support work,” Chertoff said. “We owe it to them to say look you’ve got our back, we’ve got yours. “

On the subject of growing tensions between the United States and North Korea, Chertoff said it’s unrealistic to think Kim Jong Un’s regime will disarm.

According to Chertoff, the U.S. needs to keep a whole menu of options open including pursuing a diplomatic relationship with North Korea, similar to what the US had with Cuba.

“Getting people on the ground [in North Korea] might help us calibrate better how they might respond to things that we do.”