More than half of internet users in 17 countries do not believe the web is a safe place to express their views, according to a poll.
The survey commissioned by the BBC found that 52% disagreed with the statement that "the internet is a safe place to express my opinions".
Researchers also found that one in three people do not feel free from government surveillance, with US citizens the most concerned about snooping in the wake of the National Security Agency scandal.
Belief in media freedom has also fallen in recent years, according to the study. Since 2007, internet user confidence that the media in their country has the freedom to report accurately has fallen by 19%.
The findings come after two people were jailed earlier this year for sending death threats to a journalist campaigning to have Jane Austen placed on the new £5 note.
Tony Neate, chief executive of getsafeonline.org, a government support group for using the internet safely, said: "The internet is a fantastic forum for discussion and debate, enabling us to connect with people from nations all over the world and hear differing opinions.
"In the UK we are fortunate enough to enjoy freedom of expression but this isn't the case in all countries.
"It is good to hear that people are being cautious and are aware of the dangers they may come across online.
"In general the internet is a safe place to be, but sharing our opinions with people we may not even know in real life - and who may not necessarily agree - could unfortunately leave us open to abuse.
"We advise people to think carefully about who they allow into their online networks, and to avoid using any threatening or hurtful language that may provoke others."
Doug Miller, chairman of GlobeScan, which carried out the survey, said: "The poll suggests that two of the underpinnings of modern democracies are at risk - a media seen as free and fair; and an internet safe for the free expression of views.
"The results also suggest that many of the personal freedoms that western democracies have championed in the world are actually fairly well established in the minds of citizens across these particular 17 countries.
"Ironically, it is in some of these very democracies where citizens give relatively poor ratings of some freedoms."
Last week, the Turkish government banned video-sharing website YouTube from the country, following a similar move with social network Twitter, after it claimed the sites were unfairly spreading anti-government propaganda.
The country's journalist union and bar association responded with court action citing a right to freedom of expression after audio files were leaked online allegedly linking government officials to corruption.
While Turks have found ways around the ban, neither is yet to be lifted, despite a court ruling against the government on the Twitter ban.
It comes just weeks after the man credited with the invention of the world wide web, Sir Tim Berners-Lee, said that an online bill of rights should be created in order to make the internet a safer and fairer place.
The survey was arranged by the BBC World Service as part of Freedom Live, a day of stories on the World Service exploring freedom around the world.