People holding mobile phones are silhouetted against a backdrop projected with the Twitter logo. File picture: Kacper Pempel/Reuters

Kurt Eichenwald sat down at the desk in his Dallas home office and logged onto Twitter. The prominent journalist and author was used to Internet invective – especially then, in the weeks after he posted a particularly inflammatory tweet about President Donald Trump.

More than 170 notifications awaited him when he signed on that evening, Dec. 15, 2016. But he didn’t make it past the first one: A GIF that strobed violently across his computer screen, flashing a red, yellow and blue geometric pattern behind the words “YOU DESERVE A SEIZURE FOR YOUR POSTS.”

Within seconds, Eichenwald, who has epilepsy, suffered a seizure. He would have died, he has said, if his wife hadn’t walked into the study and found him.