As human rights group Amnesty International launches a global campaign to try to halt censorship of the internet by governments, BBC correspondents report from some countries where web users face difficulties.
CHINA: RUPERT WINGFIELD-HAYES, BEIJING
Officially China does not censor the internet. According to the Chinese government, its internet regulation is no different from that in America, Britain, or anywhere else in the world.
In its quest to control the internet China has sought overseas help
China says it only blocks internet sites that are damaging, such as pornographic sites, or ones promoting things like terrorism.
The reality of China's internet is very different.
Just try logging on to the BBC News website from an internet cafe in China. You can't. The same goes for websites for The New York Times, Amnesty International, Human Rights Watch, and a host of others which could hardly be described as pornographic or "dangerous".
China probably has the most sophisticated internet monitoring and censorship system in the world. In the last few years it has spent tens of millions of dollars building what has come to be known as the "Great Firewall of China". In the past, whole websites were blocked. Today the system can block out individual parts of websites.
In its quest to control the internet China has sought help from overseas. Some large, US-based computer software companies are believed to have sold Beijing the sophisticated software needed to run its filtering system. Companies like Google and Yahoo! have also been accused of co-operating in China's internet censorship.
Google, for example, has modified its Chinese language search engine so that it does not show results for sites the Chinese government deems "harmful".
Inside China there is an even larger effort to control the country's own internet.
Internet service providers (ISPs) are required by law to monitor their own websites and chat-rooms for "dangerous content". Every ISP in China has its own staff of "web police". On top of that government employs thousands more who constantly scan the Chinese web, closing down any site or blog that is considered subversive.
For those Chinese who persist in using the internet to criticize Communist party rule, the end result can be a prison cell. Three young men were recently sentenced to prison terms of eight to ten years for using the internet to send "sensitive" information to foreign based websites.
CUBA: STEPHEN GIBBS, HAVANA
Cuba has vowed to be a force to be reckoned with in the digital era.
Thousands of Cubans are being trained in a new school for computer technology on the outskirts of Havana. Free computer clubs have been set up across the country. Even the smallest rural schools are being provided with their own terminals.
Cuba's licensed internet terminals are meant only for tourists
But at the same time the government is working hard to prevent its citizens from surfing the net without restraint. Shops in Havana might appear to sell high-quality computers, but actually making a purchase is impossible for Cubans without special approval, which is rarely granted.
Similar restrictions are in place for anyone who might want to open up an account with the state internet service provider. Exceptions include senior government officials, academic researchers, and foreigners.
The authorities say these regulations are in place in order to ensure the internet in Cuba is used for "social and collective use."
Although all Cuban media is rigorously state controlled, the government rejects accusations that it is censoring the net.
It concedes that some sites are blocked, but say these are "terrorist, xenophobic, or pornographic". Websites based in the US which publish articles by dissidents from within Cuba are generally inaccessible.
The government says that what it is doing is "prioritising" the internet, for use by sectors such as education and health. Essential, it says, given Cuba's limited resources, and limited bandwidth.
The bandwidth problem is blamed on the United States. As a result of the US trade embargo, Cuba cannot link up to the web via a direct fibre optic line. Instead it has to use more expensive satellite links.
Thousands of Cubans get around their governments restrictions and access the internet via the black market. User IDs and passwords are sold by state employees whose jobs give them legal access. Some log on via home made computers built from smuggled parts.
A legal alternative is to go to one of the cyber cafes that are being set up across the country. But these have another barrier - cost. Half an hour surfing the web costs around $3. That might be comparable to the price in other parts of the world, but in Cuba, where the average salary is $15 a month, it is substantial.
UNITED ARAB EMIRATES: JULIA WHEELER, DUBAI
In the United Arab Emirates, internet censorship centres on two distinct areas; pornography and the criticism of Gulf governments. While the majority of the multi-national population welcomes the blocking of pornography sites, the same cannot be said for the more politically motivated cases.
The UAE is one of the fastest developing countries in the world
From the UAE, attempting to access sites like www.uaeprison.com or www.arabtimes.com (published in the United States) brings up an apology for the site being blocked and an explanation; it is "due to its content being inconsistent with the religious, cultural, political and moral values of the United Arab Emirates."
It is not clear how the monopoly internet provider, Etisilat, determines what contravenes the country's values. There is a right of reply on any blocked site message though, allowing surfers to suggest it be made accessible.
For many, the censorship of sites which question, discuss or oppose the ruling families of the Gulf states and their absolute power, is anachronistic. The UAE is one of the fastest developing countries in the world, but this development is far more economic than political.
Satirical blogs, parodying the city and its residents, such as secretdubai.blogspot.com, www.dubaienquirer.com and onebigconstructionsite.blogspot.com can be found.
Internet users in Dubai's commercial free zones - like Dubai Internet City, Dubai Media City and Knowledge Village - are able to sidestep the strict state censorship by using a different proxy. The more technically savvy users in other parts of the country are also finding ways to access the banned sites they want to view.
In March, there were reports internet cafe users could have their personal details recorded and kept on file. The explanation from the authorities was that this was to curb "cyber crime" including hacking and sending spam emails, but it has brought into focus questions of personal privacy.
The opening-up of the telecoms sector which is due to allow another state-run company, Du, to operate from later this year is unlikely to change the position on blocked sites.
Perhaps one of the biggest annoyances for the mostly expatriate population in the Emirates is the inaccessibility of internet telephony sites like www.skype.com. This is widely seen as economic censorship; the state wanting to ensure continuing large profits through migrant workers making international telephone calls.