Absolutely yes, we've all been assuming security in everything we do up to this point. Knowing that the resources to defend were being deployed faster than the resources to attack, we're not afraid of our random stuff getting hacked, and there's time between zero days to patch things before they can be exploited.
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 So yes in the old world it was possible to assume a high margin of safety, in the new world given all the out of date everything out there and the speed at which anything is patched - assume nothing is secure anymore unless it is not connected to any network whatsoever - or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.
Legacy software in this environment becomes a bigger risk every day it runs.
> Absolutely yes
That's pretty strong. Recalling our pre-AI condition, there were side-channels built into our silicon, zero-day/zero-click browser+mail+IM attacks, supply chain attacks, industrial scale ransoming, mass credential leaks, commercial exploit brokers... I can't recall a time when safety could be assumed. Before even rudimentary networks were available, floppy disks were spreading viruses.
In fact, most of that is still in play. Certainly AI has reduced the cost to compromise things, but whatever period of time you have in mind where safety was an assumption was so long ago, or applicable to such a narrow subset of our information/communication age, as to be effectively negligible.