Admiral Michael Rogers Getty / Win McNamee Admiral Michael Rogers, director of the National Security Agency and US cyber commander, doesn't think that the United States will ever have a digital equivalent of Pearl Harbor.

Speaking on stage at the Wall Street Journal's WSJDLive conference, Rogers dismissed that analogy because he doesn't think that a massive cyber attacks could ever be as surprising today as the attack on Pearl Harbor was in 1941.

It's not a matter of "if," it's a matter of "when."

Rogers outlined three things that concern him the most when thinking about cyber-threats to the United States:

1. Cyber attacks that do infrastructure damage

"It is only a matter of 'when' that someone users cyber as a tool to do damage to the critical infrastructure of our nation," Rogers said.

"I'm watching nation states, groups within some of that infrastructure. At the moment, it seems to be really focused on reconnaissance and attempting to understand the characteristics of the structure, but it's only a matter of time I believe until someone actually does something destructive."

2. Data manipulation

"Historically, we've largely been focused on stopping the extraction of data and insights, whether for intellectual property for commercial or criminal advantage, but what happens when suddenly our data is manipulated and you no longer can believe what you're physically seeing?" he said.

"As a military guy, who's used to the idea that, 'I can look at a display, I can look at a set of data, and I can very quickly draw conclusions and start to make risk-based decisions quickly,' what happens if that gets called into question? I believe that's going to happen."

3. Non-state actors

"What happens when a non-state actor, who literally has no interest in the status quo — take ISIL for an example, whose vision of the world is diametrically opposed to ours — starts viewing the web as not just a vehicle to generate revenue, to recruit, to spread the ideology, but instead they view it as a weapon system?" he asked hypothetically on stage.

'This stuff is going to happen'

Rogers says that he believes that all these concerns will actually play out.

"I fully expect that during my time as the commander and the director of the NSA, this stuff is going to happen," he said. "And the nation is fully counting on us to be ready."

The NSA has faced intense scrutiny since former National Security Agency contractor Edward Snowden leaked documents revealing many of its intelligence apparatus, including global surveillance tactics.