President-elect Joe Biden on Thursday said that cyber security will be a top priority for his administration, including an investigation into a major cyber hack of the federal government that was disclosed earlier this month.

He also suggested said his response to such attacks will be aggressive.

“Our adversaries should know that, as President, I will not stand idly by in the face of cyber assaults on our nation,” Biden said.

Biden’s two paragraph statement mentions the priority he will give to cyber security and the need for a posture that includes disruption and deterrence.

“I want to be clear: my administration will make cybersecurity a top priority at every level of government—and we will make dealing with this breach a top priority from the moment we take office,” Biden said in a statement. “We will elevate cybersecurity as an imperative across the government, further strengthen partnerships with the private sector, and expand our investment in the infrastructure and people we need to defend against malicious cyber attacks.”

The U.S. government hasn’t publicly attributed the network breach, which is believed to have first occurred in the spring and be ongoing, but a Russian intelligence agency is reportedly behind it.

Biden also indicated he will take a hard line to thwart future hacks and briefly outlined the need for deterrence against cyber attacks and how his administration will operate to counter transgressions in cyber space.

“But a good defense isn’t enough; we need to disrupt and deter our adversaries from undertaking significant cyber attacks in the first place,” he said. “We will do that by, among other things, imposing substantial costs on those responsible for such malicious attacks, including in coordination with our allies and partners.”

Biden, who along with Vice President-elect Kamala Harris, receives the daily presidential intelligence brief, said that the U.S. has more to learn about the cyber hack, which he called a “massive cybersecurity breach affecting thousands of victims, including U.S. companies and federal government entities.”

Democratic leaders on the House Homeland Security and Oversight and Reform Committees on Thursday pressed the government for more information about the network breach,” highlighting media reports that described the scale and sensitivity of data that may have been stolen.

A Dec. 17 letter to John Ratcliffe, the director of National Intelligence, FBI Director Christopher Wray, and acting Homeland Security Secretary Chad Wolf from the Democrats seeks “damage assessments of this attack, including interim analyses, as soon as practicable,” and information on who committed the breach, actions to limit damage, and how the attackers will be held accountable. They also noted that there will be a classified interagency briefing for Congress about the hack on Dec. 18.

The letter was signed by Reps. Bennie Thompson (Miss.), chairman of the Homeland Security Committee, Lauren Underwood (Ill.), chairwoman of the committee’s cyber security oversight panel, Carolyn Maloney (N.Y.), chairwoman of the Oversight Committee, and Stephen Lynch (Mass.), who chairs the Oversight’s National Security Subcommittee.