Which malware encrypts files or a computer to demand a ransom for decryption?

Ransomware is a type of malware specifically designed to encrypt files or even lock a computer's system, rendering it inaccessible to the user. The primary mechanism of ransomware involves taking control of the user’s data and demanding a ransom payment in exchange for the decryption key needed to regain access to the files.

This type of malware typically spreads through phishing emails, malicious downloads, or exploit kits, seeking to maximize its impact by encrypting as many files as possible. Ransomware attacks can be particularly damaging to individuals and organizations, as they can lead to significant data loss and operational downtime while also posing challenges regarding recovery and data integrity.

In contrast, adware is software that displays unwanted advertisements; spyware secretly monitors user activity without consent; and worms are self-replicating malware that spread across networks but do not necessarily encrypt files or demand ransom. This distinction clarifies why ransomware is the correct answer in this context—its defining feature is the act of demanding payment for file decryption.