Encryption: an alien concept? Aston Fallen, CEO of Steganos, explains how you can protect your privacy by hiding your secrets in pictures and music.

There's a scene in the film ET when Elliot's mother is tidying his room. All the while, the alien he has rescued and hidden there watches her from inside a cupboard. When Elliot's mother approach the cupboard, ET shuffles to the back and stands there in fear. If he's discovered, he'll most likely be handed over to the authorities to experiment on. She opens the doors and he stares at her in astonishment as she seems to look straight through him and carries on tidying. Nestling between the children's teddies, smurfs, gonks and muppets, ET's face fits right in. Elliot's secret is safe.

We don't all have an alien in the closet, but we might have a few skeletons and everyone has a right to privacy. Just because you're happy to share your health and financial history with close family, it doesn't mean you want strangers to read it over the internet. You don't copy the whole world on your emails for the same reason that you don't receive bank statements on postcards. The threat to privacy is ever-present. As long ago as 2001, the Sircam computer virus started stealing random files from host computers, infecting them and sending them further.

The virus spread rapidly: many could not fight the temptation to open an unsolicited file from a contact that held their diary, accounts or--in the worst cases--poetry. Each time an infected file was opened, the virus infiltrated another machine.

Sircam is now under control and shouldn't present any threat to the prudent majority who use antivirus software. We still face the threat of hackers, though, and they are now backed by criminal cartels. Phishing and identity theft are fast rising crimes, fed by personal data that is often stolen from computers.

It is important to use personal firewalls, antivirus, antispam and common sense to defend your computer from malicious software. But new threats emerge all the time and the hardware is always at risk from loss or theft. If your laptop gets left on a train, there's every chance someone will boot it up to see what's on it before returning it.

The only way to be sure that somebody can't access your data--even if they can obtain a copy of it--is to use encryption.

Today you can obtain commercial encryption software that uses the same standard techniques that the US government considers good enough for its 'Top Secret' information. The 256-bit AES algorithm which powers Steganos encryption software has never been cracked. It can be easy to use too: at its simplest, the Freecrypt service will encrypt text that you enter into a form on a webpage, according to the password you provide. To decrypt it, you return to the form and reverse the process. It's free of charge at www.steganos.com.

The problem with encrypted data is that it's conspicuous. People might not be able to understand it, but they will know that there's encrypted data there and that might prompt them to misread between the lines.

The solution is to put your data--like ET in the closet--in a context where it looks perfectly natural. Using Steganos Security Suite, you can encrypt your data and then pick a host file, such as a digital photo, in which to hide it. Your encrypted data is then spread throughout the image by making tiny, imperceptible changes to the dots that make up the picture. This picture could be emailed, posted online or shared on a USB key.

People would never suspect the photo contains hidden data, and even if they did, they would still need the password to recover it. The technique is called steganography, and can be used to hide any type of data inside sound or image files. Because you're using a picture or sound recording to mask your message instead of just encrypting your text, the file sizes you handle will be larger. But by hiding your encrypted data, you add another layer of protection to ensure that your data will always be secret.

Even today, privacy need not be an alien concept.