Australians have lost millions of dollars to a phone scam demanding the payment of tax debts and threatening prison time, with authorities including the Tax Practitioners Board and police reporting their phone numbers have been appropriated as part of the hoax.
Experts warn telcos and authorities have an incredibly tough road ahead in shutting down the scammers, partly because "Voice over IP" phone setups make it so easy to hide the true phone number making the call.
On Thursday morning Camden Police Area Command in south-west Sydney issued a warning to the public after citizens reported calls from someone purporting to be from either the NSW Police Force or the Australian Taxation Office. The caller was alleging a tax debt.
"The number displayed on the caller identification is that of the local police station, and it is unclear how the scammers are utilising the actual number," NSW Police said in a statement.
The warning came just days after the Tax Practitioners Board, the regulator of tax agents, confirmed its phone number was also being impersonated in a similar scam.
In the first week of the year, tax board received around 50 calls each day from individuals reporting they had received a call from someone claiming to be a government official who was requesting credit card details in order to settle a tax debt.
"The caller ID for the calls was the TPB general enquiry number 1300 362 829 which is why the public then called us to clarify the incident," a spokesman for the board told The Sydney Morning Herald and The Age.
These reports have since dropped off, with the board saying it had swiftly announced the scam calls on social media.
Last year the Australian Taxation Office was the first organisation to confirm that its phone number had been impersonated in the tax debt scam.
On Thursday, the tax office confirmed the number of scam reports dropped between November and December 2018. However, 25,000 reports were made in December alone and 222 taxpayers lost more than $540,000 to scammers in the last month of the year.
This brings the total volume of reported tax-related scam losses to $2.8 million for 2018.
"The current scam will often demand payment of varying amounts – sometimes in the order of $5,000," an ATO spokesperson said.
There have been a number of incidents where a victim has been hit more than once by the same fake callers, the tax office said.
Telecommunications sources say most of these scam calls are originating from overseas and are difficult to protect against.
"We have arrangements in place with international carriers to monitor for suspicious calling activity on our network, and we actively block numbers we suspect are involved in call scams," a Vodafone spokeswoman said on the issue of scam calls.
An Optus spokeswoman said the provider uses automated monitoring for to detect and block suspicious calls.
A spokesman for Telstra, whose client list includes NSW Police, said part of the issue was caller ID that allowed a preferred call-back number to be identified on outgoing calls.
"Ultimately, the number displayed is set by the calling network and passed on to the caller, in addition, there are a number of Voice over IP solution providers that permit their clients to set their own display number for outgoing calls," he said.
"When [the ID service] is used correctly, it is a useful technology, when it is used incorrectly, it is often called ‘spoofing’."
None of the major telcos could point to a direct solution to stop the calls and instead encouraged awareness and for customers to protect their personal information and report suspicious calls to the authorities.
Director of cyber security research and innovation at Deakin University, Damien Manuel, said the rise of internet telephony made it difficult for authorities and telcos to stamp out scam calls.
"In the past it used to be a lot harder [to scam]. With VoIP, it's very easy for people on those networks to use a falsified ID," Mr Manuel says.
Voice over internet protocol (VoIP) is a telecommunications method that allows phone connections over the internet, rather than the public switched telephone network.
VoIP phones make it easier for scammers to mask their true numbers, while the drop in call costs has made it easier for large volumes of calls to be placed from overseas, Manuel says.
There are also legitimate reasons for spoofing a phone number, like when a business calls customers from a range of lines. This makes it difficult for telco providers to cut off this option entirely.
"There are legitimate reasons a business might need it – like in a call centre," Mr Manuel said.
At this stage, public awareness is likely a more effective route to stamping out the activity, he said.
"The best way is to become more aware that there are scams."
Emma is the small business reporter for The Age and Sydney Morning Herald based in Melbourne.
Jennifer Duke is a media and telecommunications journalist for The Sydney Morning Herald and The Age.