This paper deals with the questions of computer network, attacks, threats, network attacks, "Denial of Service", DoS-attacks, DDoS-attacks, DRDoS-attacks, mathematical model. The article presents an approach to detection of the distributed network attacks to refusal in service, the offered method increases efficiency of use of the calculated resource of a computer network at the big distributed network attacks to "Denial of Service". The paper proposes a mathematical model of compromised node and the number of all possible routes that can have an admission to access points, have done a comparative characteristics of attacks DoS / DDoS / DRDoS in computer network.