Adware is a computer program that shows you advertisements while you use it — pop-up boxes, banners along the side, a little video that starts by itself. The ads are how the maker gets paid, so the program is often free to download. People say the word with a slightly sour face: almost nobody wants adware; it usually arrives bundled with something else you did want, and then the ads will not leave you alone. It is not the same thing as a virus. A virus is built to harm the machine or break in. Adware is built to get your eyes on a paid notice. Though actually, some adware also watches what you click and sells that, and then people start calling it spyware instead. You will hear the word all the time among people who work with computers, and almost nowhere else.