Spark has warned its customers after an influx of scam calls have been targeting vulnerable Kiwis.
The technology giant says scammers have been charging "premium rates" to those who return missed calls.
In a post to customers and followers of Spark, the company has explained how the scam works in the hope of protecting vulnerable Kiwis.
"We've been seeing an influx of what are called 'wangiri' scam calls, where scammers call you, let it ring once or twice, then hang up and hope you ring back so they can charge you premium rates and pocket the money," the company wrote on Facebook.
"If you get an unexpected missed call from an unknown overseas number, it's best not to ring back.