A warning issued today by the Australian Communications Authority (ACA) highlighted the chances of unlisted and blocked telephone numbers being exposed to ISPs when accessing the internet over a phone line.
"Letting another person use such a phone line to access the internet could lead to the number being disclosed to and used by that person's internet service provider," ACA acting chairman Dr Bob Horton said.
The warning follows an ACA investigation into claims that unlisted telephone numbers, and those blocked by calling number display, had been inappropriately disclosed.
"These cases are a breach of the Calling Number Display industry code, and potentially the legislation," Horton said. "They typically happened when a person connected to an ISP from the telephone service of another person who had an unlisted number or who had blocked calling number display on their line."
The ACA advise people with unlisted or blocked numbers to be careful when allowing others to access the internet through their phone line, though Horton suggests there is no cause for alarm.
"It is not possible to establish how many people have had their telephone numbers inappropriately disclosed or used. However, when compared to the total amount of traffic between carriers and ISPs the number would be very small."
The exchange of telephone numbers between carriers is integral to the operation of telecommunications networks. However, the ACA has asked carriers to ensure that their customers know how, when and why their phone number may be disclosed to an ISP.
"It appears these practices have arisen as a result of enhancements to internet services and there is no suggestion of intentional wrongdoing on the part of carriers or ISPs," Dr Horton said.