That's a different attack vector. The attack vector that involves accessing plain text has been eliminated. An attack vector is a specific path or method that can be used to break into a system.
No. The attack vector has changed to a different attack vector.
In English, the word "the" in "the attack vector has shifted" is a definite article that refers to a single attack vector.
If your car breaks down and you switch to using a different car, would you say "the car has shifted"?
Speaking loosely, one might use "the attack vector has shifted" to mean something like "the possible attack vectors have changed", but that kind of looseness is misleading in an absolute claim like the one I originally responded to, about "all security measures". In fact, it would be more accurate to say that no security measures "shift the attack vector".