The Federal Bureau of Investigation (FBI) has launched a mega operation to copy and remove malicious web shells from hundreds of vulnerable computers in the US that were running on-premises versions of Microsoft Exchange Server software used to provide enterprise-level email service. A court in Houston has authorised an FBI operation to "copy and remove" backdoors from hundreds of Microsoft Exchange email servers that have been compromised by nation-state hackers, including from China. "Today's court-authorised removal of the malicious web shells demonstrates the Department's commitment to disrupt hacking activity using all of our legal tools, not just prosecutions," Assistant Attorney General John C. Demers for the Justice Department's National Security Division said in a statement on Tuesday.