A Low Cost Worm Detection Technique based on Flow Payload Similarity

Recently, damages of information systems by worms have been reported at global level. Signature based Intrusion Detection Systems (IDSs) are widley used to prevent these damages. To handle newly created worms, automatic signature generation techniques based on common strings in the payloads of multiple worm flows of the same kind have been proposed. Because these techniques need to use multiple strings as a signature for each kind of worm to acheive high detection accuracy, the calculation cost to detect worms is a serious issue. In this paper, we propose a novel scheme that does not use common character strings. The proposed scheme uses a 256-dimensional vector based on the appearance frequencies of 256 character codes. This vector is generated automatically and used as a mean to detect worms with low cost. In addition, we construct a cheap worm detection system by using the proposed method as the first stage analysis of conventional IDS. We evaluate the proposed scheme through experiments and present its performance.