1. A system for mitigating network attacks, the system comprising: a protected network comprising a plurality of devices; and one or more attack mitigation devices communicatively coupled to the protected network, wherein the one or more attack mitigation devices are configured and operable to employ a recurrent neural network (RNN) programmed to use a Backpropagation Through Time (BPTT) method to obtain total request probability information related to a request stream, wherein the request stream comprises a plurality of at least one of: HTTP (hypertext transfer protocol), RTSP (Real Time Streaming Protocol) and/or DNS (Domain Name System protocol) messages and wherein the total request probability information represents a probability of a respective request message string being a valid one and wherein the total request probability information related to the request stream is obtained by multiplying language-conditional character probabilities for each character included in the request message; analyze the obtained total request probability information using the BPTT method to detect one or more atypical requests in the request stream and perform, in response to detecting the one or more atypical requests, one or more mitigation actions on the one or more atypical requests in order to block an attack including: (1) determining a rate at which a source associated with a particular atypical request sends atypical requests and (2) blocking the source in response to determining that the rate exceeds a predefined threshold.