Furthermore, Ecocho's founder, Tim Macdonald, is also the co-founder of Found Agency, a high-profile search engine optimisation company that has been penalised by Google for breaking its rules in the past. Google Australia spokesman Rob Shilkin said Ecocho was barred because it broke Google's AdSense policies.

Google's policy is that publishers running Google advertising must not "compensate users for viewing ads or performing searches, or promise compensation to a third party for such behaviour". By promising to plant trees, Ecocho broke those rules.

"The site was in clear violation of our terms of service and we had previously warned the owner of past violations," Shilkin said. "We have now stopped serving ads and search results to the owner's sites."

An angry Macdonald accused Google of not applying its rules consistently, saying other green search engines using Google technology had been allowed to operate without issue. However, the other search engines, such as Blackle.com, do not explicitly promise to plant trees in return for searches. Macdonald said his company met with Google in January and went through the project "in some detail" but was not informed it would be breaking the rules.

He would not say how much profit his company was making from the site but acknowledged the cost of planting the trees would be less than the advertising revenue. "It is a business, it's not a not-for-profit, we've been very transparent about that," he said. The benefit of specialist green search engines is questionable because Google itself has invested heavily in green initiatives. Google claims it is carbon neutral, whereas the servers powering sites such as Ecocho are not.

When questioned over this, Macdonald said: "We've got a lot of users on the site who are using it from all over the world saying that it's a great idea." Another green search engine, Blackle.com, based in Sydney, has also been criticised for cashing in on web surfers' eco-guilt.

The site is a custom version of Google with a black rather than white background, which its creators said could save thousands of watts of power a year because it takes less juice for a monitor to display black than white. However, that claim was proved false by extensive testing, which found the power saving benefits were negligible or non-existent. Like Ecocho, Blackle profits from advertisements appearing next to search results. In May last year, Macdonald's company, Found Agency, saw its Google ranking tumble after it was caught unfairly manipulating its search rankings.

At the time, Found's other co-founder, Zak Asani, admitted to the Search Engine Room website that the company liked to test Google's boundaries. "We've got between 1500 and 2000 websites running at any one time that we use to test the boundaries," he said.