The sounds were detected in the Southern Indian Ocean in April.

The latest revelations are especially embarrassing for Prime Minister Tony Abbott, who declared during a trip to China in April that Australia had found the black boxes.

"We are confident that we know the position of the black box flight recorder to within some kilometres," Mr Abbott said.

But others involved with the search were more cautious.

The head of the search's Joint Agency Co-ordination Centre (JACC), retired Air Chief Marshal Angus Houston, said experts believed the sounds were consistent with a black-box flight recorder.

"The analysis determined that a very stable, distinct and clear signal was detected at 33.331 kilohertz, and that it consistently pulsed at a 1.106-second interval," Mr Houston said at the time.

''They therefore assess that the transmission was not of natural origin, and was likely sourced from specific electronic equipment. They believe the signals to be consistent with the specification and description of a flight data recorder.''

At the time there some in the  aviation community who were sceptical because the frequency identified was slightly lower than that used by black box recorders of 37.5 kilohertz.  This was put down to possible damage to the boxes or weakened batteries.

But US Navy director of ocean engineering Michael Dean told CNN that authorities now universally believed that the pings came from search equipment, not the black boxes.

"Our best theory at this point is that [the pings were] likely some sound produced by the ship ... or within the electronics of the towed pinger locator," Mr Dean said.

If confirmed by Australian authorities, the setback means the search for the missing plane is back at square one and that the best hope is for debris to be washed up to at least narrow the search area.

Experts, such as the head of the school of aviation at the University of NSW, Jason Middleton, warned trying to trace ocean currents two-and-a-half months after the accident would be extremely difficult.

"It's like looking for a tennis ball in a wheat field, Dr Middleton said. "You've looked where you think it should be, but not found it. What do you do next?"

Mr Middleton said Inmarsat had waited until well into the search to release its data on the handshake information, from the plane's communications system with its satellite.

This data was used to identify two possible arcs as the source of the plane's last communication. The northern arc over land was ruled out early and the search concentrated in the southern ocean.

But even that data is sketchy and does not include error bands, he said.

"Members of the scientific and engineering public are frustrated by the lack of information," he said.

A statement from JACC has still not been issued. A spokesman for the US Navy described DMr ean's comments as "speculative and premature".

The initial analysis of the pings was done by staff from HMAS Albatross. Experts have continued working with the data acquired by the pinger locator, Blue Fin 21, which costs $40,000 a day to operate. Some 852 square kilometres were searched but one section was too deep to search.

On the website, the Professional Pilots Rumour Network, there was a furious debate about whether the search was a waste of money

"The amount of $ wasted if this is true is insane," posted one contributor.

"From a purely financial point of view, the eventual cost of losing an aircraft full of passengers probably won't leave much change from a billion dollars. So it's worth spending at least tens of millions to try to ensure it doesn't happen again," replied another.

"In terms of what this does to the search, what do they plan on doing next? Regardless of the pings, Inmarsat's data still holds that the plane went down in that area. Now, I do suspect that now if ever would be a good time to get as many eyes on that Inmarsat raw data as possible," said another.