If you received phone calls from an unknown overseas number yesterday, you weren't the only one.
In the past few days there's been an increase in attempts at a spam technique known as 'Wangiri'.
Newshub has been contacted by dozens of people over the past 48 hours who have received missed calls, usually from numbers beginning with 0088 or 002, originating in Chad, a landlocked country in north-central Africa.
Vodafone said it registered an increase in 'Wangiri' attempts on its network, but assured customers there had been no security breach.
"In this case the fraudsters have compromised the system that manages interconnect charges internationally (interconnect charges occur when different network operators transfer customer calls across their networks)," the company said.
"The best advice we have for customers is to ignore any calls that you wouldn’t otherwise be expecting from unfamiliar country codes. Let them go to voicemail. Do not call the number back."
So how does it work?
In order for mobile phone networks across different countries to communicate with each other, there is a system set up that processes the connections and also makes sure that any international charges are passed on to the person making the call, from the country the call was made to.
For example, if it costs you $2 to call a mobile in South Africa, this system makes sure the right amount of charges are billed to you for that international connection time.
What's happened in this case is the fraudsters have compromised that system.
The fraudsters rely on you calling back that number - if you do, they pocket the cost per minute of that call.
'Wangiri' is a Japanese word meaning "one ring and cut". The scam originated in Japan.