This chapter focused on the use and implementation of backdoors and rootkits. Remember, it’s vital that you have the proper authorization before utilizing a rootkit or backdoor in a penetration test. This chapter began by introducing the powerful and flexible tool Netcat. Several uses of Netcat, including implementing Netcat as a backdoor, are covered. Cryptcat, a modern version of Netcat with the added ability to encrypt traffic between two machines, was also discussed. The chapter concluded with a brief overview of rootkits including their basic structure and use.