Adware is a portmanteau of “advertising-supported software”. This type of software displays advertisements to make money for its developer, and can show ads in the form of videos, pop-up windows, full screen ads, banner displays, and many more. Adware can also refer to a type of malicious software (or “malware”) that presents unwanted advertisements. These may occur in the form of windows you can’t close no matter how or where you click, or annoying pop-ups that never seem to end.
Adware may also monitor your browsing history or device location data to ensure that the ads it serves are relevant to you, thereby increasing the chance that you’ll click the ad. For example, if you frequently visit Target.com to see what new discounts they have available, you might find you get targeted ads in certain applications that show you amazing deals at Target.
While you might think ads are annoying at most, and you might not be bothered by the idea that someone is spying on your browsing habits to serve up targeted ads, there’s another wrinkle here. Sometimes adware and ad-supported platforms can be hijacked by criminals to serve out malware, also known as "malvertising"