Signatures of character strings in a document which may indicate a possible intrusion into or attack on a networked computer system or node thereof or other security breach are detected at high speed using a hardware accelerator within the environment of a hardware parser accelerator. An interrupt or exception can thus be issued to a host CPU before a command which may constitute such a security breach, intrusion or attack can be made executable by parsing of a document. The CPU can initiate network control measures to prevent or limit the intrusion.