Adware

An adware is a type of malware whose entire purpose is to make money for its creator through online advertising. It does this by forcing advertisements onto your screen in various forms — as pop-ups, within web pages, or even on installation screens of software. The key idea to hold onto is that adware is a business tool for its developer, not an attack on your data. It exists to generate revenue, and you are the medium through which that revenue flows.

Once an adware has managed to infect a large number of computer systems, it starts earning money in one of two ways. The first is simply by displaying advertisements to the infected users. The second is through a “pay per click” mechanism, where the adware's developer charges clients a fee every time a user clicks on one of the displayed ads. So the more machines infected, the more ads shown, the more clicks generated, and the more money the developer makes.

The book is careful to describe adware as usually annoying but harmless. It does not typically steal your files or corrupt your system the way a virus or trojan might. Its main offence is irritation — unwanted windows popping up, pages redirecting, and your browsing experience being cluttered with promotions. …