AI turns that all its head. SOTA malicious AI can create novel zero days, exploit them, spread, create more zero days, and essential hack all the things in days. So yes in the old world it was possible to assume a high margin of safety, in the new world given all the out of date everything out there and the speed at which anything is patched - assume nothing is secure anymore unless it is not connected to any network whatsoever - or even listening wirelessly - bluetooth/wifi off.