The software, called SecurePage, comes from Australian company Creative Digital Technology. Its chief operating officer, Philip Burton, is so confident it can secure web sites that he told the Australian newspaper: "We are prepared to stand behind that financially by offering a prize to universities to see if they can do what our developers haven't been able to do."

The company says none of their software developers have yet been able to alter sites that used the system.

Net graffiti

Crackers attacking Web pages replace them with their own, often embarrassing, content. Recent high profile victims are the CIA, Net security company Symantec and the US military.

SecurePage works by encrypting a copy of every page on a site, reports New Scientist. This master version is continually compared with the pages available on the Internet. If any of the content changes without authorisation, the software kicks in and restores the original using the master as the source.

Because the master is encrypted using a triple-strength version of the US government's 192-bit DES algorithm, breaking the code would require an enormous amount of time and computer power.

Crack in defences?

Bruce Schneier of Counterpane Systems, a computer security consultancy in Minneapolis, says SecurePage sounds like a good idea, but he already sees a chink in SecurePage's armour.

"Crackers would try to break the page-checking mechanism," he says. "I don't know how hard it is to do, but if they can change an equals sign to a 'does not equal' sign, they could break the system."

However, CDT chief executive Bahram Boutorabi insisted: "We can protect any Web site."