The FBI has the authority right now to access privately owned computers without their owners’ knowledge or consent, and to delete software. It’s part of a government effort to contain the continuing attacks on corporate networks running Microsoft Exchange software, and it’s an unprecedented intrusion that’s raising legal questions about just how far the government can go.

The software the FBI is deleting is malicious code installed by hackers to take control of a victim’s computer. Hackers have used the code to access vast amounts of private email messages and to launch ransomware attacks. The authority the Justice Department relied on and the way the FBI carried out the operation set important precedents. They also raise questions about the power of courts to regulate cybersecurity without the consent of the owners of the targeted computers.

As a cybersecurity scholar, I have studied this type of cybersecurity, dubbed active defense, and how the public and private sectors have relied on each other for cybersecurity for years. Public-private cooperation is critical for managing the wide range of cyber threats facing the U.S. But it poses challenges, including determining how far the government can go in the name of national security. It’s also important for Congress and the courts to oversee this balancing act.

Since at least January 2021, hacking groups have been using zero-day exploits – meaning previously unknown vulnerabilities – in Microsoft Exchange to access email accounts. The hackers used this access to insert web shells, software that allows them to remotely control the compromised systems and networks. Tens of thousands of email users and organizations have been affected. One result has been a series of ransomware attacks, which encrypt victims’ files and hold the keys to decrypt them for ransom.

The FBI is accessing hundreds of these mail servers in corporate networks. The search warrant allows the FBI to access the web shells, enter the previously discovered password for a web shell, make a copy for evidence, and then delete the web shell. The FBI, though, was not authorized to remove any other malware that hackers might have installed during the breach or otherwise access the contents of the servers.

What makes this case unique is both the scope of the FBI’s actions to remove the web shells and the unprecedented intrusion into privately owned computers without the owners’ consent. The FBI undertook the operation without consent because of the large number of unprotected systems throughout U.S. networks and the urgency of the threat.

The action demonstrates the Justice Department’s commitment to using “all of our legal tools,” Assistant Attorney General John Demers said in a statement.

The total number of compromised firms remains murky given that the figure is redacted in the court documents, but it could be as many as 68,000 Exchange servers, which would potentially affect millions of email users. New malware attacks on Microsoft Exchange servers continue to surface, and the FBI is continuing to undertake court-authorized action to remove the malicious code.

The FBI has the power to remove malicious code from private computers without permission thanks to a change in 2016 to Rule 41 of the Federal Rules of Criminal Procedure. This revision was designed in part to enable the U.S. government to more easily battle botnets and aid other cybercrime investigations in situations where the perpetrators’ locations remained unknown. It permits the FBI to access computers outside the jurisdiction of a search warrant.

This action highlights the precedent, and power, of courts becoming de facto cybersecurity regulators that can empower the Department of Justice to clean up large-scale deployments of malicious code of the kind seen in the Exchange hack. In 2017, for example, the FBI made use of the expanded Rule 41 to take down a global botnet that harvested victim’s information and used their computers to send spam emails.

Important legal issues remain unresolved with the FBI’s current operation. One is the question of liability. What if, for example, the privately owned computers were damaged in the FBI’s process of removing the malicious code? Another issue is how to balance private property rights against national security needs in cases like this. What is clear, though, is that under this authority the FBI could hack into computers at will, and without the need for a specific search warrant.