This read-write switch enables or disables the "TCP Flag and Sequence" Denial-of-Service protection feature, which checks TCP flag combinations together with the packet's sequence number for known attack signatures. Admins enable it as a more targeted variant of TCP flag filtering that also correlates a sequence number of zero with suspicious flag combinations, a pattern seen in certain crafted DoS packets. For example, a packet with SYN and FIN flags both set and a sequence number of zero would match this feature's detection pattern and be dropped.