Snort is a libpcap-based packet sniffer/logger which can be used as a lightweight network intrusion detection system. It features rules based logging and can perform content searching/matching in addition to being used to detect a variety of attacks and probes, such as buffer overflows, stealth port scans, CGI attacks, SMB probes, and much more. Snort has a real-time alerting capabilty, with alerts being sent to syslog, a seperate "alert" file, or as WinPopup messages via Samba's smbclient.
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