Guest Editor's Introduction: Unwanted Traffic: Finding and Defending against Denial of Service, Spam, and Other Internet Flotsam

The Internet is full of unwanted traffic, from junk mail, to advertising and scams that pose as social media, to fake "clicks" on ads, to denial-of-service attacks against online services. Each type causes problems in one way or another, and network operators have to work hard to identify and eliminate unwanted traffic. This issue examines the overall problem, and presents a selection of research into mitigation.