The Port of Houston, a critical piece of infrastructure along the Gulf Coast, issued a statement Thursday saying it had successfully defended against an attempted hack in August and “no operational data or systems were impacted.”

Cybersecurity and Infrastructure Security Agency Director Jen Easterly initially disclosed that the port was the target of an attack at a Senate committee hearing Thursday morning. She said she believed a “nation-state actor” was behind the hack, but did not say which one.

“We are working very closely with our interagency partners and the intelligence community to better understand this threat actor so that we can ensure that we are not only able to protect systems, but ultimately to be able to hold these actors accountable,” she said.

Sen. Rob Portman, R-Ohio, said the hack was “concerning” and said the U.S. needed to “push back against these nation-state actors who continue to probe and to commit these crimes against our public and private sector entities.”

Read more: NBC News