Despite warnings that VoIP is vulnerable to a new breed of attacks, the biggest threat remains weaknesses in general network security.

In a presentation at the RSA Conference 2006 last week, David Endler, chairman of the VoIP Security Alliance and director of security research for 3Com's TippingPoint division, said experts are aware of possible attacks that could be made against VoIP protocols, but worms, viruses and other exploits that take down servers or congest networks are the exploits that hurt VoIP in practice.

Analysis of IP voice components is key to keeping VoIP networks secure, he said. For instance, some IP PBXes are based on Windows, so any security flaws in Windows are security flaws in the voice network.

Customers also should check the management platforms of IP voice gear, Endler said. For example, some uses TFTP protocol, which requires no authentication, so hackers could glean information about a VoIP network that may be valuable in itself or provide information for future attacks.

Some VoIP phones include packet capture features that are useful in tracing packets to analyze network performance. But in the wrong hands a network of phones with this feature could be used to sniff networks for sensitive traffic such as passwords. "This could be a problem especially if the phones are connected to a hub," where they could view all traffic passing through, he said.

Logically segmenting VoIP traffic on its own virtual LAN can help keep it clear of attacks against data traffic, he said.

To protect VoIP networks, Endler recommends patching gear regularly against known threats, changing default passwords on all gear, following vendors' checklists for securing gear when installed, using intrusion-prevention gear and using VoIP-aware firewalls to protect IP PBXs.