The date should be circled in black on your computer’s calendar: internet spam is 30 years old today.

On May 3 1978, Gary Thuerk, a marketing man for DEC, a now-defunct American computer company, sent what is thought to be the world’s first junk e-mail. The unsolicited message was delivered to 393 users of Arpanet, the US government network that would become the internet, but paved the way for trillions of future missives.

Today spam has become hugely lucrative, both for the racketeers that send messages and the companies that defend against them. Spammers extracted $240 million (£121 million) in the US alone last year, according to the FBI. Eclipsing that, Ferris Research, a technology group, reckons that the global cost of fighting e-mails will hit $140 billion this year.

The use of the word comes from a Monty Python sketch but for many the joke is wearing thin: one recent study suggested that the average office worker in Britain will spend 3.5 years dealing with “irrelevant e-mail”.

In response, the authorities have launched several offensives and in 2005 Jeremy Jaynes became the first spammer to be prosecuted when a Virginia jury demanded that he serve nine years in prison.

But for the most part, the core cadre of spammers (it is estimated that 200 individuals are responsible for 80 per cent of spam) have stayed well ahead of the law. Bill Gates’s promise in 2003 that the problem would be solved by 2006 was wildly optimistic.

In the tactical race that has evolved, the spammers have developed one key weapon. In 1978, an e-mailer had to type in the address of each recipient. Today, gangs infiltrate huge numbers of public computers to turn them into “zombie machines” that are linked together to form “botnets” – vast networks that can be harnessed to churn out e-mails automatically.

The power of the botnets is staggering, with some now rivalling the capacity of the world’s largest supercomputers – machines typically used to explore the origins of the universe.

Times Recommends

• 2009: worst year for employment for 20 years
• Pound edges closer to euro parity amid rate fears
• Adams follows fashion for retailers to go under