A system for efficiently thwarting syn flood DDoS attacks on a target server including a CPU, the system comprising: network controller hardware having steering capability; and a software application to create and to configure initial steering object/s which define a steering configuration of the network controller and monitor at least one opened connection to the server, including updating the steering configuration responsive to establishment of at least one connection to the server, wherein the network controller hardware's steering capability is used to provide a SYN cookie value used for said thwarting, and to send at least one packet, modified, to the packet's source.