Imagine if every time you sent a letter, the postman made a copy. Or whenever you printed photos, the chemist kept a set for himself. This isn’t 1950s Russia but the internet today. Every e-mail you send is stored on not only your computer but also the recipient’s machine; your internet service provider (ISP) will have one too, as will the many servers that have handled your message in its travels across cyberspace. And the government is allowed, under a European commission directive, to dip into some of that data.

It’s this Big Brother vision that has inspired researchers in Seattle to create the world’s first self-destructing e-mails. Vanish, a free program developed by Roxana Geambasu and Professor Hank Levy of The University of Washington, puts an expiry date on digital messages. Eight hours after being sent, Vanish e-mails become unreadable — even to the person who wrote them.

Levy says his software is a response to the fact that the digital world has forgotten how to forget. “Storage is now incredibly cheap and there’s really no need to delete data any more,” he explains. “Personal data last for a long time.” A recent survey found that a fifth of Americans had written something online that they regretted, while almost one in eight teenagers had posted nude or revealing photos of themselves. In the digital age, these acts remain a permanent, and potentially life-ruining, blot on the record.

Personal e-mails, perhaps containing bank or credit card details, can also linger online for years. “You can’t ensure an e-mail is really deleted because you don’t really control it,” Levy says. “Your e-mail company might store it on back-up tape. A judge could issue a subpoena to get old e-mails or a hacker could break in and steal them. They could be revealed with a system error or someone could simply have their laptop stolen.”

Encrypting your e-mails is no guarantee of privacy, either. In 2007, Hushmail, a company that describes itself as offering the most secure webmail service, admitted to deciphering coded messages and turning them over to Canadian police as part of a drug investigation. In the UK, suspects have been forced to turn over e-mail encryption passwords to the courts or face jail.

Vanish would make such events impossible. Like other encryption programs, the new software scrambles text into a string of nonsensical letters and numbers. Then comes the clever bit: Vanish splits the digital key to decode the message into 10 pieces. These fragments are then hidden in plain sight, on 1.5m randomly selected computers — part of a network of machines spread across more than 200 countries. Not only does this make it almost impossible for hackers to locate the key fragments; it gives Vanish messages their limited lifespan, because as users log off from this network and their computers refresh their memories, the number of key fragments online decreases. After eight hours, on average, enough fragments will have been erased for the message to be unreadable — to the writer, the recipient or a court.

At the moment, Vanish requires both parties in an e-mail or chatroom to install the program and to use the Firefox web browser to communicate. You can then use any webmail service or social network to compose a message, highlight the text you want to keep private, choose “Create Vanish message” from a pop-up menu and send the message as usual. At the other end, recipients see only a page of scrambled text until they select “Read Vanish message”.

That doesn’t mean your message is totally secure. You are still trusting the recipient not to make a copy of the e-mail during its eight-hour existence; and, Levy says, Vanish will not render you invisible to the authorities. “There are government agencies that are big enough to threaten this,” he says. “It’s mainly meant for individuals and individual privacy.”

The makers of Vanish are not standing still, however. The next version will allow users to increase the lifespan of e-mails in multiples of eight hours, allowing users to create messages lasting a day, a weekend or a month.

“We live in a world where it’s possible to remember everything that everyone ever does,” Levy says. Vanish may not make today’s digital world any less scary but at least you can finally forget about old e-mails coming back to haunt you, years — or even days — in the future.

Try Vanish free at vanish.cs.washington.edu

Explore Tech & Web

• Personal Tech

• The Web

• Gadgets & Gaming