Censoring the Internet works through legal restrictions and through physical blocking with the use of software and hardware. Web filtering software uses keyword blocking and blacklists to restrict access to particular websites and categories of websites. Firewalls are software that act as barriers between the Internet and individual networks. They allow access to content deemed safe and block all other content.
Internet censorship is used to suppress information that can be published or viewed. It is implemented by governments or private companies working on behalf of governments. Some countries routinely censor significant amounts of information. Censorship by national governments sometimes occurs in response to or in anticipation of major events, including riots, protests and elections.
Some countries use laws, surveillance and software to restrict the Internet. As of 2014, China uses a filtering system referred to internationally as the "great firewall of China." The system restricts access in real time by constantly searching new websites for banned content. In Cuba, the Internet can only be viewed through public access points; private access is banned.
Specific technologies used to censor Internet access include filtering and redirection of domain name systems, in which incorrect or disallowed domain names are blocked. In uniform resource locator filtering, URLs are scanned for restricted keywords and are blocked accordingly. Internet access is sometimes restricted by turning off all network routers.