Define 'malware'.

Malware refers to malicious software specifically created to disrupt, damage, or gain unauthorized access to computer systems and networks. Its primary purpose is harmful, aiming to exploit vulnerabilities in devices, whether through viruses, worms, trojans, or ransomware. This definition aligns perfectly with the given choice, as it captures the intent and function of malware in the cybersecurity landscape.

The other options describe software that serves different purposes, either positively impacting system performance, functioning as a protective measure like anti-virus programs, or monitoring user behavior, which is often associated with tracking software or applications, but does not reflect the malicious intent that characterizes malware. The distinction between malicious and benign software is crucial in cybersecurity, positioning the definition of malware as encompassing threats that actively seek to harm systems and data integrity.