Some 1000 international calls were fraudulently routed through a Western Australian business' telephone account last week, after its poorly configured TDM phone system was compromised.
The attack was likely to be a case of toll fraud, scammers would charge users to place premium international phone calls then funnel them through weak phone systems, leaving victims to foot the bill.
Local telecommunications accounting firm TIM4biz detected the calls and advised the company.
Telstra then banned outbound international calls from the business, saving it from a potential phone bill that for other victims regularly run into tens -- and sometimes hundreds -- of thousands of dollars.
"We detected an aggressive and sustained attack on a client's phone system that commenced at 7:30pm on March 19 and continued through to 7:30am the following day," Tim4biz director Cyril Eliopulos said.
Western Australian police reported that attacks on Voice over IP phones early last year cost three businesses $70,000. In 2009, criminals rang up phone bills exceeding $120,000.
Misconfigured and unpatched telephone systems were most at risk of phone fraud. Many devices had web-facing functionality activated at the time of purchase which were protected using default settings.
Those settings known to and targeted by scammers.
Many brands have refused to alter the out-of-the-box settings. Some including Cisco have issued user-hardening guides which show how to turn off risky functions.
"Manufacturers should make it easier for users," Eliopulos said.
He cited a recent case of a Brisbane company that was similarly defrauded after scammers exploited vulnerabilities in its unnamed but then fully patched modern phone system.
He did not wish to name the affected system or any others because the company works with vendors to address problems, he said.
Eliopulos recommended businesses disable international call functionality and voice mail remote access of internet-accessible phone systems.
Those organisations that require international calling should limit access to specific numbers and ban calls to premium lines.