Australian investigators have helped bust an international scam in which consumers were duped into paying to clean their computers of bogus viruses.

US officials say 14 companies using staff posing as Microsoft employees convinced consumers their computers had virus infections which could cause massive problems.

The Federal Trade Commission says six scareware operations have had their assets frozen following an investigation in cooperation with Canada, Britain, Australia and New Zealand.

FTC chairman Jon Leibowitz said the schemes involved calls to consumers in English-speaking countries from call centres in India, informing consumers of bogus infections.

"The tech scam artists that we're talking about today have taken scareware to a new level of virtual mayhem," he said.

"At one level, it's like a bad Bollywood movie, but at another level it's a rip-off of consumers."

The groups also used online ads which informed computer users of the infections and then sold "fixes" at prices ranging from $49 to $450.

The Australian Communications and Media Authority (ACMA) was part of the investigation and says an estimated $25 million was taken by the scammers in Australia alone.

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ACMA chairman Chris Chapman says consumers still need to remain vigilant.

"I'm not suggesting they're not going to start up again, but part of the orders include, for example, phone companies in the US being precluded from providing services to these people so it's an enormous disruption," he said.

"Their assets have been frozen, it means they've got to start up again."

Helen told the ABC that she was was harassed by the scammers.

"I keep them talking and simply say 'this is marvellous that you can detect this' until I finally have to tell them we don't have Microsoft on our computers," she said.

ABC/AFP