A system is called "intrusion resistant",
if it, as a whole,
continues to adhere to it's predifined rules
even in case of a part of the system components violate
(accidentally or by malicious intent).
The aim of intrusion resistance
is to counter-ballance for the consequences
of continued operation of an embraced device
under violation of normaly system-guaranted assumtions
(e.g., forged data, access rights).
Known ways to achieve that goal are
tamper proofed hardware
and systems based on ByzantineAgreement.
Remark: Eventually there is no such thing like tamper proofed hardware, just more complication to do so.