They forcefully show you ads of different companies or products and make money from it. Adware is a malware with money earning motive underlying beneath it. This happens because you might have accidentally clicked on some pop-up caused by adware on your computer and you accidentally added an extension to your browser.
Adware is the reason you get re-directed to an unknown search engine while you open the browser. Adware is responsible for unwanted ad pop-ups in your computer.
