Why does NAT improve security?

It says NAT, but we will replace it with NAPT

"From the phrase ""rise"", we can read the nuance that ""before"" and ""after"" are better."In this case, "after" is "after the introduction of NAPT," but what is the situation with "before"? Readers didn't take the class directly, so they have no choice but to estimate.

If "Previous" is "Pre-NAPT":

From the wording of the question, it seems that the assumption is that the internal machine should use a local address and never use a global IP address, but in order to communicate from the internal machine to the outside of the organization without NAPT, the internal machine must also be given a global IP address.So

• Previous: The global IP address used by the internal PC can be inferred from the outside and directly accessed from outside the organization
• After: I can guess the local IP address of the inside PC, but the NAPT router prevents me from accessing it

That's going to increase security.
I don't know if the instructor meant that.

In my understanding, the inside local address cannot communicate with the outside global address in the first place, so
I felt there was a problem before the security level went up.

Typically, when communicating from an inside local address to an outside global address, it communicates through the gateway.
NAT translates inside local and outside global addresses.

Therefore, it is not impossible to communicate with an external global address.
This can be communicated from the inside local address to the outside global address and
You can receive the answer, but you cannot communicate directly from the outside to the inside.
We know one IP address from the outside, but there are multiple PCs connected inside.
Each has an inside local address, which is invisible to the outside world.
Therefore, it is strong against external attacks.

If you know the inside local address, how can you access it and cause security issues?
Is that so? Now that I know the internal local address, I feel that there is no big problem.

First of all, which is better, when some kind of attack is carried out or when no attack is carried out at all?
Depending on the effectiveness of any attack, there are various security holes in the operating system that can follow.If this attack is enabled, password, credit card
Information may be stolen or data may be erased.
If you're not attacked at all, it's safe.

The real problem is that user information on some site has been stolen or credit card information has been stolen.
This is attacking security holes.
Attacks
because various websites are assigned fixed global addresses. From the side, it's convenient.

Please refer to this as well.
https://www.infraexpert.com/study/ip10.html