Which of the following describes adware?

Adware is primarily defined as software that automatically displays or downloads advertising material when a user is online. This type of software often presents unwanted advertisements in various forms, such as pop-ups, banners, or within other applications or websites. The main characteristic of adware is its focus on delivering ads without the user’s consent, which can lead to an intrusive user experience and can sometimes result in system slowdowns or unwanted changes to browser settings.

While some adware may collect user data to tailor advertisements based on behavior, this is not its defining feature. The other choices relate to different types of software functionalities: monitoring user behavior is characteristic of spyware, blocking internet traffic is a function associated with firewalls, and encrypting files pertains to security software designed to protect data from unauthorized access. Thus, the correct choice accurately captures the essence of what adware does in terms of user experience.