Thirty years ago next week, Gary Thuerk, a marketer at the now-defunct computer firm Digital Equipment Corporation, sent an email to 393 users of Arpanet, the US government-run computer network that eventually became the internet. It was the first spam email ever.

That commercial message, sent on 3 May 1978, drew a swift and negative reaction. Recipients complained directly to Thuerk, who had made no attempt to hide his identity, and DEC was reprimanded by the Arpanet administrators.

Nevertheless, the email was a portent of things to come. Today, spam makes up 80 to 90% of all emails sent – around 120 billion messages per day – and is a multi-billion dollar industry.