DHS Secretary Janet Napolitano admitted that there have been some instances in which hackers have “come close” to shutting down parts of the nation’s critical infrastructure.

Napolitano said these types of network intrusions on financial systems, transportation networks and other assets key to America’s day-to-day functioning are one of her top concerns in an age when cyberattacks are growing exponentially.

“It could theoretically cause a loss of life, but also a huge economic loss,” Napolitano said at a Washington Post Live conference Thursday morning. “We’ve seen attempts on Wall Street, transportation systems, things of those sorts.”

Dealing with cyberattacks is an uncharted territory for the government and poses a whole new set of defense questions that still lack answers. Napolitano called for the creation of a national and international framework to address cyberattacks.  

Napolitano said that jihadists, such as Al Qaeda, are more focused on attacking the U.S. through aviation and explosive devices rather than cyberattacks. But she added that there are others in the world that may not be jihadists but “have other motivations” and technical capabilities that are looking to attack the U.S.