The security of information systems is the most important principle that can also be said that the most difficult, because security must be maintained throughout the system. At the beginning of this article we are going to introduce basic principles of security. The securities of distributed systems are divided into two parts: A portion of the communication between users and processes is concerned with examining issues such as authentication, message integrity and encryption will be discussed. In the next section, we will examine the guaranteed access permissions to resources in distributed systems. In addition to traditional access solutions, access control in mobile codes will be examined.