The spread of malicious agents in the form of worms has severe implications for network performance. Damage can be as minimal as slowing down a network with excessive, unwanted traffic, or as serious as putting attacker-defined code on a system to cause any type of malicious damage.

Current methods to stop the propagation of malicious agents rely on signature recognition to prevent hosts from being infected. However, the latency between the introduction of a new virus or worm into a network, and the implementation and distribution of a signature-based patch can be significant. Within this period, a network can be crippled by the abnormally high rate of traffic generated by infected hosts.

Connection-rate filtering based on virus throttling technology is recommended for use on the edge of a network. It is primarily concerned with the class of worm-like malicious code that tries to replicate itself by using vulnerabilities on other hosts (weaknesses in network applications behind unsecured ports). Agents of this variety operate by choosing a set of hosts to attack based on an address range (sequential or random) that is exhaustively searched, either by blindly attempting to make connections by rapidly sending datagrams to the address range, or by sending individual ICMP ping messages to the address range and listening for replies.

Connection-rate filtering detects the network behavior of malicious code that tries to create a large number of outbound IP connections on an interface in a short time. When a host exhibits this behavior, warnings can be sent, and connection requests can be either throttled or dropped to minimize the barrage of subsequent traffic from the host. When enabled on the switch, connection-rate filtering can help reduce the impact of worm-like malicious code and give system administrators more time to isolate and eradicate the threat. Thus, while traditional worm and virus-signature updates still need to be deployed to hosts, the network remains functional and the overall distribution of the malicious code is limited.