Server computers generally run applications software or provide sets of services to many different users. Sometimes the users will have the ability to log in to the server, whereas in other situations only the administrators can log in. Server computers generally run multiuser operating systems such as UNIX and the various server versions of Windows.
Computer attacks are many and subtle. Sometimes an attack may have a limited objective, such as access to a particular file or application, but more frequently the objective is to gain the ability to install new software or run applications with superuser privileges.