What is the purpose of this?

The line
set noexec_user_stack= l
should be added to the /etc/system file to prevent an executable stack while executing user
programs. What is the purpose of this?

A.
help prevent core dumps on program errors

B.
help programs to execute more quickly by keeping to their own memory space

C.
log any messages into the stack log

D.
help make buffer-overflow attacks more difficult

Explanation:
How to Disable Programs From Using Executable Stacks
Purpose: Prevent executable stack from overflowing.
You must be in the root role.
Edit the /etc/system file, and add the following line:
set noexec_user_stack=1
Reboot the system.
# reboot

Reference: How to Disable Programs From Using Executable Stacks