Windows EFS can help users avoid the above risk easily. However, this barrier can be easily avoided if an attacker gains physical access to users’ computers. Without EFS, when operating system is running, access to files or folders goes through OS-controlled user authentication and access control lists. To be more specific, it ensures that any files or folders is stored in encrypted form and decrypted only by an individual user and an authorized recovery agent. How does it work? The technology works together with NTFS permissions to grant and refuse computers access to files and folders in some Windows operating systems. What is EFS? Short for Encrypting File System, EFS is introduced as a transparent public key encryption for the version 3.0 of Windows NTFS (New Technology File System).