No technology is without its flaws and same is the case with the VoIP system. With increasing popularity and reliability, it has become prone to hackers. Since many things go through phone line, hackers can intercept private information. Since there has been no dangerous attack on an IP system yet, therefore, most customers of VOIP are more likely interested in cost and quality than security. However, new security devices are being developed with increasing security threats, which can be incorporated into all-in-one applications to protect whole information networks. Such devices that protect the whole network reduce individual expenses that are imposed by VoIP security threat.

VoIP converts analog signal to digital signals and send them through internet. It opens up the telephone network to attacks from hackers, who can intercept and listen to phone conversations and steal sensitive information like credit card number and bank details. They can even launch denial of service attacks and shut down an ongoing conversation, or send virus over the internet to disrupt the services. The biggest threat hackers are imposing is manipulation of VoIP networks for making free calls. Then there are some hacking websites that let people to control the phone number that appears on the receiver's caller-id display this is called caller-id spoofing. VoIP loges information on call management boxes, these boxes are vulnerable to hackers' attacks and viruses, this can have a down falling effect on an organization's reliability and cost them a lot of money for data retrieval and security upgrading. Waiting for something to happen and trying to solve the problem after that can be costly for an organization and for its customers. Therefore, before making the move to VoIP, companies need to acquaint themselves with the security issues about this new technology and plan protection in advance.

Encrypting VOIP voice traffic, using Layer 2Tunneling protocol and Secure Sockets Layer, firewalls, and restricting access by using an alternate for VOIP traffic are a few of the ways to cut any VOIP security issues. In addition a company should secure the network by putting in place layers of security to protect at all levels including servers, conversations, computers, and telephones. Just as you protect your PC with virus software, firewalls etc similarly you can protect a VoIP system with similar measures. L2TP acts as a 'data link layer protocol' for tunneling network traffic between two callers over the Internet. SSL allows client/server applications to communicate in a way designed to prevent eavesdropping, tampering, and message forgery. These techniques prevent the hackers from capturing the information packets as they pass through the internet.