''We didn't know what to expect - all we really wanted was to draw attention to the coalmine plan,'' said activist Jonathan Moylan, speaking on behalf of the group called Front Line Action on Coal.

Mr Moylan played a key part in the hoax, including impersonating an ANZ spokesman when contacted by Fairfax. He later apologised for lying - after Whitehaven Coal shares had temporarily dropped in value by $314 million.

The activists discussed the plan last week, then invested $25 in buying an internet domain name - ANZcorporate.com - which also allowed them to use a fake email address that fooled several major media organisations.

On Saturday, according to the time stamp on the document, Mr Moylan created a fake press release from ANZ that said the bank had decided to pull out of a $1.2 billion loan that would have been used to finance a new coal mine in Leard Forest. The document, which was simply a reworked version of a real ANZ press release, was sent to journalists at 11.44am on Monday.

Minutes later, the Whitehaven share price was tumbling by 8.8 per cent, as some shareholders assumed the proposed coal mine was no longer viable.

Mr Moylan's mobile number was listed on the press release, under the name ''Toby Kent''. Mr Kent is a real employee in the ANZ corporate affairs section - though well-informed journalists might have known the real Mr Kent has a British accent, whereas Mr Moylan is from Newcastle, NSW.

Mr Moylan, an Esperanto speaker and French translator, had rehearsed some polished lines about ANZ's corporate responsibility to impersonate Mr Kent. In the event, only Fairfax called the mobile phone number on the fake press release to check the story.

Nonetheless, an inaccurate story about ANZ's supposed pull-out from the coal project was written for the AAP news wire, and versions of the story quickly appeared on major news websites.

ANZ immediately denied it. At 1.01pm, the Front Line Action on Coal group issued a second press release admitting the hoax, and saying it had done so to draw attention to the environmental problems that it said would be caused by the mine.

Mr Moylan said the group had got the idea of the hoax from several stunts from activists groups in the US, particularly one by ''The Yes Men'' which had ''punked'' US chemicals company Union Carbide.

Other groups have recently used hoax letters even videos to highlight environmental issues. Greenpeace partnered with ''The Yes Men'' earlier this year in a campaign to discredit oil drilling in the Arctic, which also included fake video clips on YouTube, an elaborate spoof website, and a fake Twitter account.

Mr Moylan, who has appeared in court several times charged with trespass offences after illegally entering coal and aluminium sites in NSW, said he didn't regard the hoax as successful.

''We don't measure success in terms of Whitehaven or anyone losing money,'' he said.

''Success for us is what happens in reality, not in terms of abstract numbers.

''It's about whether the water table gets destroyed, whether the forest gets bulldozed, whether farmers can continue farming the land or not.

''So, no, we haven't succeeded.''