(CNN) -- Hundreds of websites posted messages opposing online government surveillance on Tuesday, as activists planned live protests and other gatherings in cities all over the world.
Social news giant Reddit, blogging site Tumblr and Mozilla, the makers of the Firefox browser, were among the most high-profile sites to take part in the online protest. Much of it targeted surveillance by the National Security Agency in the United States.
"Today we must fight back against mass, suspicionless surveillance. Today we must protect both our civil liberties and the digital tools connecting us all," Reddit said in a blog post. "Indiscriminate bulk surveillance programs by the NSA and their allies ... violate the First and Fourth Amendments of the U.S. Constitution, which protect citizens' right to speak and associate anonymously, guard against unreasonable searches and seizures, and protect their right to privacy ... .
"In addition to individual privacy issues, these surveillance programs are damaging for online businesses like reddit. These programs undermine the basic freedom, innovation, and economic opportunity that the Internet enables."
The Internet's biggest players, like Facebook, Google and Wikipedia, stayed out of Tuesday's protests, at least publicly. But others didn't pull any punches with their objections.
The live events scheduled for Tuesday include rallies in San Francisco, Chicago, Los Angeles, London, Stockholm, San Juan and other places.
The coordinated global protest was announced in January, on the eve of the one-year anniversary of the death of Aaron Swartz.
Swartz, an online activist and co-creator of Reddit and RSS feeds, committed suicide in 2013 while facing indictment on charges that he stole millions of online documents from the Massachusetts Institute of Technology.
"Aaron showed us that being a technologist in the 21st century means taking action to prevent technology from being turned against the public interest," said Roy Singham, chairman of tech company ThoughtWorks, where Swartz worked at the time of his death, said in a news release. "The time is now for the global tribe of technologists to rise up together and defeat mass surveillance."
Last month, President Barack Obama announced reforms to the way government agencies collect information both online and via telephone records. Among other changes, he said analysts will need a judge's approval to access phone records and that tech companies will have more freedom to report the kinds of information the government requests.
Obama also said the public will be given some access when government agencies ask judges for data to "provide an independent voice in significant cases" that have been conducted entirely in secret up until now.
Many Web activists were not satisfied with Obama's changes, saying they didn't go far enough.
Other events Tuesday include a "street theater and light art" event in Austin, Texas, at which people are encouraged to " dress up like an NSA agent and pretend to record our fellow Austinites just like the real National Security Agency does every day in a less visible form."
A Carrollton, Texas, event invites concerned people to "come out and show Big Brother what it looks like when the people get mad."
Tuesday morning, Reddit's mainpage featured images of Benjamin Franklin along with this quote: "They who would give up essential liberty, to purchase a little temporary safety, deserve neither liberty nor safety."
Mozilla's home page featured a link to a tool that claims to show Web users some of the entities tracking their online activity.