Because of the proliferation of hackers, so in order to prevent malicious attacks, firewall software emerged. But we should be able to use the firewall software correctly, let it really serve us.
Firewalls have defined the level of security, in order to give different users different security control, but many users do not particularly understand these, in order to secure, blindly to the security level to "high security level", that the higher the security level the better. Not really. If your computer is too safe, you will find that online games will not be able to start, and the video program will not be able to access the online video files (this is a great loss for ADSL users). So what do all the security levels mean?
Low security level: The computer will open all services, but prohibit access to files, printer sharing services on the Internet. Applies to users who provide services on the local area network. This is the maximum level of freedom, so it is limited to "network gurus".
Medium security Level: Prohibit access to system-level services (such as HTTP, FTP, etc.). The machines inside the LAN only allow access to file, printer sharing services. Use dynamic rule management to allow open port services for programs that are authorized to run, such as online gaming or video telephony software. and can guarantee for example to send and receive mail and transfer files of the general user, so generally this security level is the default value.
High Security level: The system will screen out all the ports open to the outside, prohibit access to provide all services, the common Trojan programs and attacks to intercept, provide a strict control of the network access capabilities; For users who simply surf the web. Of course the network game you can not play.
In addition, all security levels control the access of the application to the network.