Reporters with the Target 11 news program reported on the case of Heather and and Courtney Kuykendall's mobile phones, whose handsets were allegedly used to spy on and threaten them.

"They are listening to us and recording us. We know that because they record us and play it back as a voice mail," the couple told reporters.

The Channel 11 reporters were sufficiently intrigued to contact a professor with Carnegie Mellon University - mobile phone expert Priya Narasimhan - to show how the monitoring was carried out.

According to the TV news station, specialist software that sells for around $300 can be uploaded to a suitable smartphone and will then monitor any voice calls using a technique known as off-phone extension monitoring.

The software essentially allows a third party to dial into the phone and listen in to any calls made or received, Infosecurity notes.

The monitoring software also reportedly allows remote access to text messages sent and received on the mobile.

The software appears to operate by taking a direct feed from the mobile phone's microphone and speaker, and then relaying the data stream to a remote location.

Unconfirmed reports suggest that the Blackberry smartphone is susceptible to the remote monitoring software, although other smartphones may also be liable eavesdropping from the Java-driven software, Infosecurity understands.