Triggers when a series of TCP packets with both the SYN and FIN flags set have been sent to the same destination port on a number of different hosts. This could, for example, be a sweep of many hosts to find out which ones can receive mail or telnet sessions.
This is indicative that a reconnaissance sweep of your network may be in progress. The use of both the SYN and FIN flag is abnormal, and could indicate an attempt to conceal the sweep.
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