Internet censorship works in a variety of ways, often combining technical and social engineering to prevent the spread of material that repressive governments find offensive. At its most basic, many countries operate filters that block particular websites from being accessed. While these blockages are flagged in some countries surfers in Saudi Arabia are told the page they are trying to access is censored, for example others simply choose to make blocked sites appear to be unavailable or broken.
In addition to website filtering, internet service providers employ blocks or operate surveillance on certain hot-button keywords. This will often involve the blocking of websites containing banned terms, or the inability to send and receive communications containing those words. In some cases, data on the attempts to access banned information are transmitted back to authorities, who use that information to arrest, prosecute or persecute offenders.
Most countries that heavily censor the internet deploy a mixture of technical countermeasures and more traditional authoritarian repression. Some also ''encourage'' companies that operate inside their borders to take over censorship duties, a move that often proves more effective than attempting to cope with wide censorship centrally.
In some countries, including China, website owners and internet service providers afraid of possible sanctions by the government often prove more censorious than the authorities themselves.
But with heavy restrictions in place on internet usage in parts of the world, a complex game of cat and mouse has evolved between the bureaucratically determined and the technologically astute. No sooner has a firewall been imposed than users start thinking of ways around it.
Here is some of the software censored populations are using to overcome firewalls.
Freegate
Chinese computer scientists in the United States created the Global Internet Freedom Consortium to allow followers of the banned Falun Gong religious group to evade internet censors and to provide email delivery services to China for US government agencies and non-government organisations. They maintain an anti-censorship network called DynaWeb. Users can find settings for the software via email or automated messages from DynaWeb's instant messaging account. If manual settings are a bit intimidating, they also produce the Freegate software, which taps into the DynaWeb network. You can either download and install it on your computer, or install it on a USB memory stick and run the software on another computer. The benefit of the latter is you don't need to carry around a computer and running it from the USB stick leaves no trace on the computer you're using. Iranian users rushed to use the software, and traffic from Iran tripled during the recent crackdown, according to Dr Shiyu Zhou, of Global Internet Freedom Consortium.
Tor
Freegate only works on Windows computers, but Tor, which not only allows users to evade filters but cloaks a user's identity, works on most machines. Tor can also be run off a USB stick. It works on a similar idea as Freegate, using a network of computers to reroute traffic around obstacles thrown up by government censors.
Firefox plug-ins
Several plug-ins for open-source browser Firefox have also been produced to help get around web filters. FreeAcess Plus allows access to several popular social networking sites and some blocked sites in countries like Iran. The Access Flickr plug-in allows access to the popular photo-sharing site in countries like Iran and China.
Proxies
Another way technically savvy people can help is to act as proxies. A proxy provides internet users an alternative path to the internet, free of censorship. It has proven useful during the recent Iranian crackdown. Internet proxies work by acting as a go-between for internet users and the wider internet. Businesses often use them to protect internal networks. To circumvent censorship, a computer acting as a proxy takes a request to a blocked website from a user and retrieves the site on their behalf. Eventually even the proxies can be blocked, but that becomes difficult if enough users set up proxies. Users set their computers to act as a bridge or relay on networks like Tor, which offers detailed instructions on how to set up a proxy site.
Many of these techniques have proven invaluable in keeping the censor at bay. But there is one slight drawback. Most work by funnelling traffic through alternative internet gateways or forwarding internet requests through a number of computers to protect your identity. Speed suffers as a result.
Guardian