The average medieval castle featured layers of defence. Multiple wall rings were constructed so that there was no single intrusion point. However, these walls could be rendered useless by that most unpredictable of enemies: the insider
Internet telephone service's appeal as a cutting-edge technology for cutting phone costs is convincing more and more people to ditch their landlines and go hi-tech with Voice over Internet Protocol. VoIP companies like Vonage are growing rapidly, with their promise of nifty new features and lower monthly phone bills. Vonage, one of many Internet telephone service providers, says that about 1500 people sign up for its service alone per month. But some computer security experts say that, just as with wireless networking, VoIP's rapid-fire adoption will be closely followed by revelations of security vulnerabilities and electronic attacks.