With the increasing development of computer and communications technology growth and increasing needs and development of information systems security. The problem of security must be approached with greater caution. With the development of computer and communication technologies have developed numerous tools to protect files and other information. A set of tools, procedures, policies and solutions to defend against attacks are collectively referred to as computer network security. It is necessary above all to define and learn about the concepts of attack, risk, threat, vulnerability and asset value. During the design and implementation of information systems should primarily take into account a set of measures to increase security and maintenance at an acceptable level of risk. In any case, there is a need to know the risks in the information system. Sources of potential security problems are challenges and attacks, while the risk relates to the probable outcome and its associated costs due to occurrence of certain events. There are numerous techniques help protect your computer: cryptography, authentication, checked the software, licenses and certificates, valid authorization... This paper explains some of the procedures and potential threats to break into the network and computers as well as potential programs that are used. Guidance and explanation of these programs is not to cause a break-in at someone else's computer, but to highlight the vulnerability of the computer's capabilities.