1. A method for controlling multi-tiered mitigation of cyber-attacks, comprising: monitoring at least availability and load of each protection resource in a multi-tiered communication network, wherein each tier in the multi-tiered communication network includes a plurality of protection resources having capacity and security capabilities set according to the respective tier; for each protection resource, computing a current aggregated load metric (ALM); determining based on at least one of the computed ALM and security capabilities of a respective protection resource, if the respective protection resource assigned to a protected entity can efficiently handle a detected cyber-attack against the protected entity; and selecting at least one new protection resource to secure the protected entity, upon determining the protection resource cannot efficiently handle the detected cyber-attack, wherein the selection is based on at least one of the computed ALM and a security capabilities of the at least one protection resource.