pplication, or set of devices at carriers, enterprises, and homes that screens incoming and internal traffic to prevent hackers from accessing files. Firewalls deny hackers access by allowing only designated users to access networks. In an organization's network, firewall software is installed on routers and appliances. For additional protection, organizations that use their carrier's firewall protection have onsite firewall protection, as well. Firewalls provide networks partial protection against Distributed Denial-of-Service (DDoS) attacks and intrusion. They use various techniques including address filtering, which looks at a user's IP address and accepts or rejects messages based on that address. Important applications might contain their own firewalls for extra protection. Communications can also be restricted to certain addresses. Firewalls contain hundreds of ports and can filter on a port-by-port basis. In addition, they can be programmed to recognize applications and content and pass them through the firewall using a www.TechnicalPDF.com specific port. However, even with these filtering capabilities, DDoS attacks can congest access to the organization's files. Firewall ports can be virtual as well as associated with physical equipment within the firewall. A virtual port is programmed to allow certain traffic such as VoIP calls to pass through the firewall to its destination. A virtual port is represented in software. Because employees use their laptops at home to surf the Web and then bring them into work, corporations monitor internal transmissions as well as communications from the Internet. Many organizations program employees' remote computers to reach only locations on the Internet deemed secure to avoid contamination from Internet locations that have viruses that can spread to the corporate LAN. Firewalls don't protect against, for example, new (black day) viruses and all e-mail spam. Corporations often subscribe to security services that keep them posted about new software attacks. The security s