The objective of this invention is to ensure that programs that generate and send data packets are well behaved. This invention discloses a method and system that consist of an end station and a network interface, such that, the network interface is capable of determining the authenticity of the program used by the end station to generate and send data packets. The method is based on using a hidden program that was obfuscated within the program that is used to generate and send data packets from the end station. The hidden program is being updated dynamically and it includes the functionality for generating a pseudo random sequence of security signals. Only the network interface knows how the pseudo random sequence of security signals were generated, and therefore, the network interface is able to check the validity of the pseudo random sequence of security signals, and thereby, verify the authenticity of the programs used to generate and send data packets.