Anyone who's ever left a comment on a website or signed up for an online service such as webmail or photo-sharing will know that part of the process inevitably involves deciphering twisted words or numbers from what is known as a CAPTCHA.

Of course, rather than being designed to make life difficult for you, CAPTCHAs are supposed to make it impossible for automated spam programs to masquerade as humans and start spreading their unwanted advertising junk.

Junk mail flood

And that's precisely how they worked until this year, with millions of websites around the world relying on the 11-year-old technology to keep the tide of spam at bay.

However, all is not well with CAPTCHA and 2008 may turn out to be its last year in the job after the spammers finally found a way to crack the code and put their spambots to work.

By April, all of Hotmail, Yahoo Mail and Gmail had seen their CAPTCHA defences breached by automated programs that let the spammers flood in, leaving major web companies scrabbling for an alternative.

One such option that looks promising is SpamFizzle from researcher Michael Kaplan. Indeed Kaplan claims the technique is "likely invulnerable to automated decryption".

Spatial awareness

SpamFizzle uses 3D models of objects and people, then randomly labels parts of them with letters of the alphabet. The idea is that anyone signing up for a service might be asked to say which letters are found on, for example, the right hand of a running man or the back of the leftmost chair.

Such spatial perception quizzes are currently insurmountable problems for software, so next time you sign up for a new email account or post a blog comment, you'll know why you're being asked about furniture and body parts.