bro -- Open-source, Unix-based Network Intrusion Detection System<hr>
<a href="http://bro-ids.org">http://bro-ids.org</a><hr>
Bro is an open-source, Unix-based Network Intrusion Detection System
(NIDS) that passively monitors network traffic and looks for suspicious
activity.  Bro detects intrusions by first parsing network traffic to
extract is application-level semantics and then executing event-oriented
analyzers that compare the activity with patterns deemed troublesome. Its
analysis includes detection of specific attacks (including those defined
by signatures, but also those defined in terms of events) and unusual
activities (e.g., certain hosts connecting to certain services, or
patterns of failed connection attempts).
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