RECENT research is suggesting that Google's audio capture is the latest in a string of CAPTCHAs to have been defeated by software, PCWorld. com reported.

A CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart), is the squiggly hard to read letters that many sites now have you enter to prove you are human.

Image CAPTCHAs for Google, Windows Live, and Yahoo! have been broken in recent months, and is believed to account for the increasing levels of spam that are coming from webmail services that those companies provide.

The development of software to automatically interpret CAPTCHAs brings up a number of problems for site operators - in particular, software that can rapidly interpret the tests effectively negates any barrier to entry that the CAPTCHA once represented.

Audio CAPTCHAs are a means to allow vision-impaired Internet users access to site areas that they would otherwise be denied to. Much like the image counterparts, audio CAPTCHAs apply distortion to a set of numbers or letters that are read out in a small audio file.

Both of Google's CAPTCHA tools have now been defeated by software and it should only be a matter of time until the same can be said forMicrosoft and Yahoo!' s offerings.

Even with an effectiveness of only 90 per cent, any failed CAPTCHA can easily be reloaded for a second try.

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