A common network access procedure is a method allowing a user to access resources provided by a remote system. There are several threats, ranging from eavesdropping to destruction of data, that are identified with common network access services. Common network access services and their threats are discussed in the following sections. It is not uncommon for a cracker to install an altered version of a common network access program. The altered program may accept a special input sequence for the purpose of spawning a shell for the cracker, or, the altered program may be used to capture passwords.