Which of the following can be identified as malware?

C is identified as malware because ransomware specifically refers to a type of malicious software designed to block access to a computer system or data, often by encrypting files, until a ransom is paid. This type of attack is intended to extort money from the victim and falls squarely under the category of harmful software, which is the definition of malware.

In contrast, antivirus software and firewall applications are defense mechanisms designed to protect systems from malware and other threats, while a system optimization tool is typically used to improve system performance and does not have malicious intent. This distinction is crucial for understanding the characteristics that define malware versus protective or utility software.