a) The following questions are related to operating system security: i. Describe countermeasures to defuse intruders and malicious software. (3 marks) ii. Contrast the compile-time defenses and runtime defense to counter buffer overflow attacks. (3 marks) iii. Select and justify at least three tools to conduct ethical hacking and penetration test. Explain how the selected tools can be used to perform a security audit on this client's computers/devices. (3 marks) iv. Discuss several steps to prevent zero-day exploits