As part of the operation, which authorized the activity for email servers in the United States, the FBI copied and removed "one early hacking group's remaining web shells" from affected targets. The Web shells could have been used to maintain and increase unauthorized access to networks if left on the compromised machine, say officials, who call the operation "successful."
News of the operation arrives roughly six weeks after Microsoft disclosed critical Exchange Server flaws that have since been used to target thousands of networks around the world. An attacker could leverage the vulnerabilities to break into an unpatched server and steal its data.