Which of the following best describes malware?

Malware, short for malicious software, is specifically crafted to cause harm, disrupt, or gain unauthorized access to computer systems and networks. This encompasses a wide range of malicious activities, including stealing sensitive information, damaging files or systems, and facilitating other criminal activities like cyberattacks. The primary goal of malware is to exploit vulnerabilities in systems or networks for nefarious purposes.

In contrast, the other options describe benign or helpful software tools. Enhancing system performance usually relates to optimization software that improves a computer's efficiency rather than causing harm. Monitoring user activity can be part of legitimate surveillance or parental control software but does not fit the malicious intent characteristic of malware. Backup software is designed to protect and preserve data, making it fundamentally different from malware, which aims to compromise systems and data integrity.