The web blackout from July 9 will be enforced by the US Federal Bureau of Investigation (FBI), which is shutting down a number of web servers through which infected users' web request traffic has been travelling. It's shutting them down following an investigation into a sophisticated internet fraud ring which used the servers to manipulate people's web browsing.

The malicious software, or malware, changes a user's Domain Name System (DNS) settings on their computer, diverting all web requests through servers the FBI seized in November but has been temporarily maintaining to ensure internet services were not disrupted. This maintenance will finish on July 9, meaning computers still infected will face internet troubles.

"It is likely that users infected ... will be unable to connect to the internet when the temporary DNS solution is switched off," the dns-ok.gov.au website states.

Bruce Matthews, manager of the ACMA's e-Security division, said since November last year the watchdog had seen more than 10,000 Australian internet users infected with the "DNSChanger" malware.

Mr Matthews said that the ACMA worked with Australian internet service providers to try and reduce the number of infected users since it knew about the malware but said the number had only been reduced by a few thousand since November.