There is disclosed a method for determining malicious files in a network traffic, the method executable by a server. The method comprises: receiving the network traffic from a data communication network, retrieving a plurality of files from the network traffic, analyzing the plurality of files in order to detect at least one suspicious file, running the at least one suspicious file in at least one virtual machine, the at least one virtual machine associated with a set of the status parameters, determining changes in the set of the status parameters of the at least of one virtual machine, analyzing the changes in the set of status parameters using a set of the analysis rules such that to classify the at least one suspicious file as a malicious file based on the changes in the set of status parameters being indicative of the at least one file being the malicious file.