A method and packet filtering system that accelerates the packet classification problem is made. Using spectral analysis of rules and using real time spectral analysis of packets, it is possible to determine very quickly that a packet does not match any of the possible rules that have been defined. That is to say, using the packet filtering of the invention, there is no possibility of a false negative decision; when a packet is determined not to match any rule, the work of a packet classifier is complete. This method and system are also capable, with a high degree of accuracy, of determining that the packet has matched one of the defined rules, so that the packet may be then directed to a packet classifier to determine the specific rule it matches.