Iranian hackers infiltrated the control system of a small dam near New York City in 2013, according to a Wall Street Journal report.

Citing former and current U.S. officials and experts familiar with the matter, the Journal reports that concerns about the attack reached the White House.

The still-classified dam intrusion targeted the Bowman Avenue Dam, a small 20-foot tall concrete slab used for flood control near the village of Rye Brook, N.Y.

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Citing an unclassified Homeland Security summary of the case that doesn’t specify the type of infrastructure by name, the Journal reports that hackers are believed to have gained access to the dam through a cellular modem. Two people familiar with the incident told the Journal that the summary refers to the Bowman Avenue Dam.

Hackers didn’t take control of the dam but reportedly probed the dam’s system.

Iranian officials didn’t respond to a request from comment from the Journal. The Department of Homeland Security told the Journal that it doesn’t comment on specific incidents and the FBI declined to comment.

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The hack comes amid ongoing fear of a cyberattack on critical U.S. infrastructure such as power grids. The Stuxnet worm, which crippled Iran’s nuclear production in 2010, highlighted hackers’ ability to target industrial systems. Stuxnet was said to be a joint U.S./Israeli effort.

Earlier this year, security researchers at Kaspersky Lab unearthed malware that can place spying software in hard drives. One of an arsenal of tools created by a shadowy collection of hackers dubbed “the Equation Group,” on account of their sophisticated encryption algorithms, the malware prompted fears of widespread computer eavesdropping. The report noted links between the Equation Group and the developers of the Stuxnet worm.

Iran’s Revolutionary Guard is behind a slew of recent cyberattacks against the White House, according to the Journal.