Security have figured out how to spy on Verizon Wireless mobile phone customers by hacking into signal-boosting devices, known as femtocells, sold by Verizon. The specific devices aer used by consumers in order to boost wireless signals indoors.

The finding was first reported by Reuters news agency. Researchers from iSEC demonstrated how they can eavesdrop on text messages, photos and phone calls made with an Android phone and an iPhone by using a Verizon femtocell that they had previously hacked.

They did not to disclose how they had modified the software on the device, but they plan to give more elaborate demonstrations two weeks from now at the Black Hat and Def Con hacking conferences in Las Vegas.

Verizon said it has updated the software on its signal-boosting devices to prevent hackers from copying the technique of the two experts.

Still, the two researchers said they are able to use the hacked femtocell to spy on Verizon phones even after Verizon released that update because they had modified the device before the company pushed out the software fix.