Computer network is a system that connects different or similar devices into a single unit. Network management includes proper configuration, connectivity and control of network elements. Computer networks maintenance is a complex and demanding job as a computer connected to a computer network is no longer an isolated system, but subject to the interaction of other systems. Today's computer networks are increasingly based on the TCP / IP set of protocols because of simplier definition of the device network address and because of the possibility of connecting to the Internet to use its online services. Planning protection system is based on examination of all known threats and proposed solutions as a result of a compromise. Malware is the common name for all software that was created specifically for the purpose of infiltration or damaging computer systems. The types of malware are Spyware, Adware, Trojans, Worms and Viruses. Many security mechanisms, such as Antivirus programs, computer networks security protocols, access control, encryption and watermarks can be used to protect documents. Effective protection does not mean applying only one solution, but a combination of different methods of protection.