On Tuesday the Department of Justice announced the FBI was given approval to access hundreds of computers across the United States running vulnerable versions of Microsoft Exchange Server software to remove web shells left by hackers who had earlier penetrated the systems... "The FBI conducted the removal by issuing a command through the web shell to the server, which was designed to cause the server to delete only the web shell (identified by its unique file path)," it adds. A web shell is, in essence, an interface the hackers have opened up so they can communicate with the vulnerable system at a later date. The announcement said the FBI action did not patch the underlying systems themselves, or remove any other additional malware.