What type of malware is characterized by displaying unwanted advertisements while users are online?

Adware is a type of software designed to display advertisements to users while they are browsing the internet. It generates revenue for its developers by automatically showing advertisements in various forms, such as pop-ups, banners, or even embedded ads within programs. The primary characteristic that defines adware is its focus on delivering ads that may degrade the user experience, leading to the term "unwanted advertisements." While some adware might collect user data to better target ads, its main function centers around advertisement delivery.

In contrast, a virus is a type of malware that attaches itself to legitimate programs and files, often replicating itself and spreading to other systems. Spam refers to unsolicited messages, typically sent via email, and isn’t categorized as malware. Spyware is a different form of malware that secretly monitors user activities and collects personal information, rather than focusing primarily on advertising. Therefore, adware is the most accurate choice when identifying malware specifically associated with unwanted advertisements online.