This Counter64, in Protocol Data Units, counts application PDUs with either an invalid header size or an invalid payload size as determined by local security policy, requires deep packet inspection to be implemented, and accumulates since the firewall's last reboot. An admin uses it to spot malformed or policy-violating PDU sizes crossing the firewall, which can indicate malformed clients, misconfigured applications, or attempted exploits relying on oversized payloads. A steady baseline count with an occasional sharp spike would be worth investigating as a possible probing attempt using oversized packets.