Question

which of these is a way of making applications less vulnerable to hacking?
make deny the default
make allow the default
apply the principle of greatest privilege
have a single point of defense

Explanation:

Making "Deny" the default means that by default, access or certain actions are not permitted. This reduces the attack - surface as unauthorized access is blocked by default, making the application less vulnerable. Making "Allow" the default would increase vulnerability as more actions would be permitted by default. Applying the principle of greatest privilege gives more access than necessary, increasing risk. Having a single point of defense is a bad practice as if that point fails, the system is compromised.

Answer:

make Deny the default