Which of the following is NOT considered malware?

A browser extension is not considered malware because it is typically a legitimate piece of software designed to add functionality or features to a web browser. While some browser extensions may have malicious intent, the term "malware" specifically refers to harmful software created to exploit, damage, or gain unauthorized access to systems and data.

In contrast, viruses, worms, and Trojans are all types of malware. A virus attaches itself to clean files and spreads through the system when the infected file is executed, whereas a worm is a standalone malicious program that replicates itself across networks without needing to attach to another program. A Trojan disguises itself as legitimate software but contains harmful code that can compromise systems. Each of these types of malware is designed to disrupt, damage, or gain unauthorized access to systems, which sets them apart from legitimate software like browser extensions.