Types of Events Detected
The types of events most commonly detected by NBA sensors include the following:
Denial of service (DoS) attacks (including distributed denial of service [DDoS] attacks). These
attacks typically involve significantly increased bandwidth usage or a much larger number of packets
or connections to or from a particular host than usual. By monitoring these characteristics, anomaly
detection methods can determine if the observed activity is significantly different than the expected
activity. Some NBA sensors are aware of the characteristics of common DoS tools and methods,
which can help them to recognize the threats more quickly and prioritize them more accurately.
Scanning. Scanning can be detected by atypical flow patterns at the application layer (e.g., banner
grabbing), transport layer (e.g., TCP and UDP port scanning), and network layer (e.g., ICMP
scanning).
Worms. Worms spreading among hosts can be detected in more than one way. Some worms
propagate quickly and use large amounts of bandwidth. Worms can also be detected because they can
cause hosts to communicate with each other that typically do not, and they can also cause hosts to use
ports that they normally do not use. Many worms also perform scanning; this can be detected as
previously explained