Cisco confirmed it is possible to eavesdrop on remote conversations using Cisco VoIP phones. In its security response, Cisco says: "an attacker with valid Extension Mobility authentication credentials could cause a Cisco Unified IP Phone configured to use the Extension Mobility feature to transmit or receive a Real-Time Transport Protocol (RTP) audio stream."

Cisco adds that Extension Mobility authentication credentials are not tied to individual IP phones and that "any Extension Mobility account configured on an IP phone's Cisco Unified Communications Manager/CallManager (CUCM) server can be used to perform an eavesdropping attack."

The technique was described by Telindus researcher Joffrey Czarny at HACK.LU 2007 in Luxembourg in October.

Cisco has published some workarounds to this problem in its security response.

Also in October, two security experts at hacker conference ToorCon9 in San Diego hacked into their hotel's corporate network using a Cisco VoIP phone.

The hackers, John Kindervag and Jason Ostrom said they were able to access the hotel's financial and corporate network and recorded other phone calls, according to a blog on Wired.com.

The hackers used penetration tests propounded by a tool called VoIP Hopper, which mimics the Cisco data packets sent at three minute intervals and then trades a new Ethernet interface, getting the PC - which the hackers switched in place of the hotel phone - into the network running the VoIP, according to the blog post.

The Avaya configuration is superior to Cisco, according to the hackers, because you have to send requests beyond a sniffer. Although it can be breached the same way, by replacing the phone with a PC.