Common UwS distribution tactics include: misleading ads such as trick-to-click, ads disguised as download or play buttons, bad software downloader practices, hijacked browser default settings, annoying pop-up messages, annoying system pop-ups, and more. The FTC recently recently announced that the FTC recently decided to enforce strict characterizes and characterizes UwWS as a form of malware. We believe 1 in 10 Chrome users have hijacked settings or unwanted ad injectors on their machines; there is lots of work still to be done.”]
Source: https://security.googleblog.com/2015/12/year-one-progress-in-fight-against.html