A normal TCP segment header has at least one flag control set.
A TCP segment with no control flags set is an anomalous event.
Operating systems respond to such anomalies in different ways.
The response, or even lack of response, from the targeted device
can provide a clue as to the target's OS type.
When this option is enabled, if the device discovers such a
header with a missing or malformed flags field, it drops the
packet.
The attribure records the detection of TCP without flag set packets.