Which of the following is not a security risk?

The correct option is Firewall.

To understand why a firewall is not a security risk, let us analyze each of the options step-by-step:

1. Firewall:
A firewall is a network security system or software that monitors and controls incoming and outgoing network traffic based on predetermined security rules. It establishes a barrier between a trusted internal network and an untrusted external network (such as the Internet) to prevent unauthorized access. Because a firewall is designed to protect systems from threats, it is a security measure rather than a security risk.

2. Hacking:
Hacking involves identifying and exploiting weaknesses in a computer system or network to gain unauthorized access. Since hacking is an unauthorized activity that compromises data and system integrity, it is a major security risk.

3. Phishing:
Phishing is a cyberattack method where perpetrators send fraudulent messages—often disguised as legitimate emails—to trick victims into revealing sensitive information like login credentials, passwords, or financial details. This is a significant security risk based on social engineering.

4. Pharming:
Pharming is a malicious practice where users are secretly redirected to a spoofed (fake) website, even if they typed the correct URL into their browser. This is typically achieved by exploiting vulnerabilities in the Domain Name System (DNS) or by altering host files on a local machine. Pharming is a critical security risk used to steal credentials and personal data.

In summary, while hacking, phishing, and pharming are all malicious activities that pose direct threats to computer systems and data, a firewall is a defensive tool used to mitigate such threats.