Which of the following is a category of malware?

Ransomware is indeed a category of malware that poses significant threats to systems and data. It is a type of malicious software that encrypts a victim's files, making them inaccessible until a ransom is paid to the attacker. This category has gained notoriety due to its mechanisms that leverage social engineering tactics to infect devices, often spreading through phishing emails or compromised downloads.

In the context of other choices, a firewall and antivirus are security measures designed to protect systems from various threats, including malware, but they are not malware themselves. Data Loss Prevention refers to strategies and tools that protect sensitive data from loss or unauthorized access, rather than being a type of malware. Thus, ransomware stands out clearly as a specific threat in the broader category of malware.