Charles Seife is a pop historian who writes about mathematics and science, but his abiding theme, the topic that makes his heart leap like one of Jules Feiffer's dancers in the springtime, is human credulity.

In Sun in a Bottle (2008), he observed the scientists who chased low-temperature fusion down the rabbit hole. In Proofiness: The Dark Arts of Mathematical Deception (2010), he delivered his thesis in his first sentence: "If you want to get people to believe something really, really stupid, just stick a number on it."

Seife's new book, Virtual Unreality, is about how digital untruths spread like contagion across our laptops and smartphones.

He delivers a short but striding tour of the many ways in which digital information is, as he puts it, in a relatively rare moment of rhetorical overkill, "the most virulent, most contagious pathogen that humanity has ever encountered".

He has a lighter touch, though every so often he pounds his ideas so remorselessly that he makes you wonder why we online addicts aren't all twitching and frothing at the mouth like Gwyneth Paltrow in Contagion.

One of Seife's bedrock themes is the Internet's dismissal - for good and ill - of the concept of authority. On Wikipedia, your Uncle Iggy can edit the page on black holes as easily as Stephen Hawking can. Serious reporting, another form of authority, is withering because it's so easy to cut and paste facts from other writers, or simply to provide commentary, and then game search-engine results so that readers find your material first.

Seife worries about how easily fringe ideas find purchase on the Internet, where previously they would have perished from lack of oxygen.