What characteristic best describes adware?

Adware is best characterized as software designed to collect user information to display advertisements tailored to the user's interests. This type of software typically tracks web browsing habits, search preferences, and other online behaviors to build a profile that enables more targeted advertising. The primary goal of adware is often to generate revenue for its developers through advertising rather than performing harmful actions like data encryption or extensive monitoring.

The other characteristics listed do not accurately reflect the nature of adware. While monitoring network traffic is associated with malware or certain legitimate software for analysis, it is not a primary function of adware. Similarly, software that is solely focused on providing online games lacks the inherent objective of data collection for advertising purposes. Finally, encrypting user data is a characteristic related to ransomware, which has a different purpose than adware. Thus, the defining feature of adware is its role in collecting user information to optimize advertising, making option C the most appropriate choice.