Acting ACA chairman Dr Bob Horton said that the thwarted spammers had reacted to an ACA warning in late March that the Act was due to come into force in April and that they would need to comply with it.
"The ACA's initial focus was on spammers allegedly sending high volumes of offensive unsolicited material including pornography and marketing for products such as herbal Viagra," said Horton.
"At the end of the first three months of the Spam Act it appears that these particular major players have stopped operating in Australia because complaints about them stopped when the Act came in on 10 April".
The international anti-spam watchdog Spamhaus has confirmed the closure of the spammers. "As recently as last week, Spamhaus reported that there has been little or no activity by these particular major Australian-based spammers of offensive material since they were warned by the ACA about the new law," he said.
Since the Act came into force, Horton said the ACA has received about 30,000 reports of spam, including more than 300 formal complaints. "As a result of these complaints the ACA has contacted more than 100 businesses advising them to improve their e-mail and SMS marketing practices to comply with the Act," he said.
"Most of the complaints we receive are about businesses continuing to send commercial messages to a recipient who has tried to unsubscribe. Clearly many businesses still need to test and fix their unsubscribe feature".
Although most businesses have reported changes to their practices to ensure that they complied with the new law, the ACA is investigating "several cases where the response to our warnings and advice has been unsatisfactory," said Horton. "Four formal notices have been sent to parties under investigation".
Failure to comply with the Spam Act can result in a hefty fine reaching thousands of dollars, or a prosecution penalty of up to AU$1.1 million per day for repeat offenders.
"Spam is a global problem that requires a global solution. While Australia is cleaning up its own backyard, only two per cent of global spam that Australians receive comes from Australian sources. The key to improvement in the Australian user experience depends on all nations taking similar action to counter spam," said Horton.
Australia has already signed memorandums of understanding with Korea, the USA and the UK.
Last week Horton chaired a meeting of nations and private sector representatives at the International Telecommunication Union in Geneva to discuss cooperation in countering spam.
"The meeting concluded with strong interest in international cooperation and joint action by regulators, industry and consumers, and confidence that spam could and would be effectively countered in the medium term," he said.