Threats to VOIP systems include but are not limited to denial-of-service (DoS) attacks, eavesdropping, man in the middle (MITM) attacks, call hijacking, spoofing, and call fraud in addition to many others. These threats are becoming more prevalent against VOIP providers, forcing the need for continual improvement to counter the increasing sophistication of hijacking, hacking, and listening devices. The most common are DoS and eavesdropping, which are briefly discussed below.

Denial-of-Service attacks are becoming commonplace even in the early adopter VOIP providers. To counter these attacks Cisco and other network hardware

In terms of security and reliability, Comcast Digital Company has invested the equivalent of 25% of the total annual revenues of Vonage in their platforms and security. Their alliances with Cisco and Symantec as members of each of these company's advisory councils and beta testing programs are also evidence of the company's focus on reliability and security. Further, the company has testing the latest generation of firmware on VOIP routers and next generation software from Nortel and Cisco. Comcast has a budget for IT infrastructure that is 25% of Vonage total sales.

Vonage also is investing in VOIP security and has several engineers who are working on and filing patents on breakthrough technologies for security. Like Comcast, Vonage also participates in advisory councils with Cisco, Nortel, and Symantec. The scaling of servers to the European market is forcing the company to implement VOIP firewalls throughout entirely new geographies and countries, which has added to services costs. Vonage also has not yet found the E-911 initiative easy to support, they are being sued in Texas for not telling VOIP customers they had to register with E-911; their existing VOIP infrastructure in that state did not support it by default yet customers were lead to believe it was a standard and supported feature.

Both VOIP providers Vonage and Comcast Digital Cable are aggressively pursuing the goal of having a robust and highly secure VOIP network. For Comcast, the stakes are very high as they are primarily a cable television provider company whose profitability depends on their ability to reduce customer churn. One of the best approaches to reducing churn is to have customers buy more than one service, and VOIP is the perfect add-on for them to residential subscribers.

Eavesdropping is also a very common threat that VOIP partners encounter, as hackers can record to audio files conversations and post them to the Internet. According to Ghaffar, 2004 a proven strategy for countering ea

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