This is a 64-bit counter tracking the number of packets discarded because they were identified as part of a fragment-based attack. Because fragment attacks are a known denial-of-service technique that exploits reassembly logic, a nonzero and rising count is a security signal worth investigating rather than routine traffic loss. For example, an admin spotting a sharp jump in hh3cMecErrFragAttack from a particular source would treat it as a potential attack and consider blocking that source.