Investigators believe that Iranian hackers were probing the electronic defenses at a dam above New York City, it’s being revealed today.

Watch below:

From the Wall Street Journal:

Iranian hackers infiltrated the control system of a small dam less than 20 miles from New York City two years ago, sparking concerns that reached to the White House, according to former and current U.S. officials and experts familiar with the previously undisclosed incident.

The breach came amid attacks by hackers linked to Iran’s government against the websites of U.S. banks, and just a few years after American spies had damaged an Iranian nuclear facility with a sophisticated computer worm called Stuxnet. In October 2012, then-Defense Secretary Leon Panetta called out Iran’s hacking, prompting fears of cyberwar.

The still-classified dam intrusion illustrates a top concern for U.S. officials as they enter an age of digital state-on-state conflict. America’s power grid, factories, pipelines, bridges and dams—all prime targets for digital armies—are sitting largely unprotected on the Internet. And, unlike in a traditional war, it is sometimes difficult to know whether or where an opponent has struck. In the case of the dam hack, federal investigators initially thought the target might have been a much larger dam in Oregon.

Many of the computers controlling industrial systems are old and predate the consumer Internet. In the early digital days, this was touted as a security advantage. But companies, against the advice of hacking gurus, increasingly brought them online in the past decade as a way to add “smarts” to U.S. infrastructure. Often, they are connected directly to office computer networks, which are notoriously easy to breach.

These systems control the flow in pipelines, the movements of drawbridges and water releases from dams. A hacker could theoretically cause an explosion, a flood or a traffic jam.