In computing, a firewall is a network security system that monitors and controls the incoming and outgoing network traffic based on predetermined security rules. A firewall typically establishes a barrier between a trusted, secure internal network and another outside network, such as the Internet, that is assumed not to be secure or trusted. Firewalls are often categorized as eithernetwork firewalls or host-based firewalls. Network firewalls are a software appliance running on general purpose hardware or hardware-based firewall computer appliances that filter traffic between two or more networks. Host-based firewalls provide a layer of software on one host that controls network traffic in and out of that single machine. Firewall appliances may also offer other functionality to the internal network they protect such as acting as a DHCP or VPN server for that network.
Having a personal firewall can quell the jitters you might have about your computer getting attacked. An Internet connection, especially an always-on type like broadband, is the entry point for hackers who want to get to your computer. A firewall polices your connection and is an essential tool in a basic computer security arsenal, along with an anti-virus tool. The book "Network Security First-Step" likens a firewall to an Internet border security officer because of its role in disallowing the wrong things from entering your computer from a network or the Internet.
A firewall monitors all of the traffic entering your computer network. A two-way firewall does double duty and monitors the traffic exiting your network as well. Information is sent over networks in packets. Those packets are what the firewall investigates to determine if there's something they contain that's potentially hazardous to your network's security. Even you as the sender could transmit something bad, without knowing it, which is why it's important to have a firewall police the contents.
A firewall helps block Trojan horses. These types of intruders latch onto your computer files, and then when you send out a file, they go along for the ride to do more damage at the destination. Trojans are especially dangerous because they silently transmit what they uncover about you to a Web server. You're oblivious to their presence until strange things start happening to your computer. A firewall blocks them from the outset, before they have a chance to infect your computer.
Having a firewall keeps hackers out of your network. Without firewall security, a hacker could get a hold of your computer and make it a part of what's called a botnet, which is a large group of computers used to conduct illicit activity, such as spreading viruses. While hackers represent an extreme group, individuals who you may not suspect, such as neighbors, can also take advantage of an open Internet connection you may have. A firewall prevents such peeping-tom intrusions.
Having firewall security will reduce the risk of keyloggers monitoring you. A keylogger is spyware software that cyber criminals try to put on your computer so they can target your keystrokes. After they can identify what you're typing in and where, they can use that information to do the same thing. This knowledge can help them log in to your private online accounts.