When you connect to the Internet, you can access web sites on the Internet, but other users on the Internet can also access information on your computer and potentially infect it with harmful viruses and worms. For more information, see "Avoiding Viruses and Other Harmful Attacks" on page 330.
You can prevent this by activating Windows Firewall, another security layer of protection. A firewall is a security system that creates a protective barrier between your computer or network and others on the Internet. Windows Firewall monitors all communication between your computer and the Internet and prevents unsolicited inbound traffic from the Internet from entering your computer. Windows Firewall blocks all unsolicited communication from reaching your computer unless you specifically allow it (unblock) to come through, known as an exception. For example, if you run a program, such as Windows Live Messenger that needs to receive information from the Internet or a network, Windows Firewall asks if you want to block or unblock the connection. If you choose to unblock it, Windows Firewall creates an exception so the program can receive information. For details, see "Setting Up Windows Firewall" on page 136.
If you send and receive e-mail, Windows Firewall doesn't block spam or unsolicited e-mail or stop you from opening e-mail with harmful attachments. To protect your computer from these attacks, see "Protecting Against E-mail Attacks" on page 194. Windows Firewall helps block viruses and worms from reaching your computer, but it doesn't detect or disable them if they are already on your computer or come through e-mail. To protect your computer, you need to install antivirus software.
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