Packet data comparator as well as virus filter, virus checker and network system using the same

A packet data comparator which detects match or mismatch between packet data inputted from a data path connecting among information processing means and stored data, comprising:

• branch means which branches the inputted packet data into at least first, second and third branched packet data to perform processing in parallel;
• an additional pattern matching unit which has a function of comparing the first branched packet data with a part of the stored data, and performs matching with collation patterns stored in a rewritable storage area;
• a fixed pattern matching unit which has the function of comparing the second branched packet data with the part of the stored data without using any operating system, and performs the matching with a logical operation by hardware processing using a logical device which has been configured based on known collation patterns;
• a notification packet matching unit which has the function of comparing the third branched packet data with the part of the stored data, and detects a notification packet;
• and
• a match detection aggregation unit which aggregates respective matching results from said additional pattern matching unit, said fixed pattern matching unit and said notification packet matching unit,
• wherein the fixed pattern matching unit has less delay and performs the monitoring more rapidly than the additional pattern matching unit, and
• a result in which the match or the mismatch has been detected is outputted from said match detection aggregation unit.