One young man sitting in a forest used a laptop and a mobile phone to temporarily wipe more than A$314 million ($394 million) from the value of Australia's Whitehaven Coal on Monday morning.
The Australian Securities and Investments Commission is now making inquiries into the elaborate hoax, in which anti-coal campaigners issued a fake media release and impersonated a corporate affairs spokesman from ANZ Bank.
The media release said ANZ had reversed a decision to provide a A$1.2 billion loan to Whitehaven, and sparked a sudden sharemarket sell-off when it was emailed to journalists at 11.44am. The company's price dropped about 8.8 per cent and Whitehaven was put into a trading halt.
It resumed trading on Monday afternoon, after news of the hoax spread. The stock recovered to its original price of A$3.52.
"We will be speaking to the people involved," ASIC said in a statement.
Whitehaven said it would be "investigating any legal action that may be available to it and its shareholders".
A NSW Police spokeswoman said police were yet to receive a formal complaint about the hoax but would investigate if asked to do so by ASIC.
The hoax was co-ordinated by Jonathan Moylan, a 24-year-old Newcastle man with a history of participating in protests against coalmines and an aluminium smelter in NSW.
He has taken part in a protest camp against coalmining in Leard State Forest - the site of the proposed Whitehaven mine, near Narrabri in NSW - for the past 158 days. The hoax was conceived and created from the forest camp, with its sporadic internet connection, he said.
He and and an activist group, Frontline Action On Coal, created the fake media release, using a real ANZ statement as a template, bought a website name and a dummy ANZ email address for about A$25 on the internet.
When contacted by Fairfax Media, Moylan initially posed as a corporate affairs spokesman for the ANZ Bank.
He later apologised for lying and tried to justify the hoax by saying it was worth it to draw attention to the environmental problems that the open-cut coalmines would probably cause.
"We have been campaigning against ANZ for a while now because we believe that if customers of the bank knew their money was being used to finance coal they'd object to that," he said.
Asked if he had qualms about lying to the public to achieve environmental ends, he said: "Our primary concern is the impact of this mine on the environment ... A lot of people were taken in by it but when you compare the cost of that to the health of our forests and farmlands, it justifies it."
He said the group had based the hoax on stunts perpetrated by a US group called the Yes Men, which had embarrassed the chemicals company Union Carbide, and Australian comedians from The Chaser.
Whitehaven's managing director, Tony Haggarty, said in a statement: "Whitehaven treats matters such as the fraudulent hoax announcement by Mr Moylan very seriously.
"The integrity of the information provided to the public regarding Whitehaven goes to the heart of the market's integrity and directly affects the price of Whitehaven shares, as well as our many shareholders. Whitehaven will liaise with the ASX and ASIC in relation to Mr Moylan's irresponsible and ill-conceived conduct and trusts those authorities to take the appropriate action."
ASIC has confirmed it is looking into whether the hoax breached any of the rules governed by the commission.
The hoax is the third time in six months that an ASX-listed company has had its share price affected by hoaxes.
Similar stunts affected David Jones in July and MacMahon Holdings in October.
- Sydney Morning Herald