THERE IS a new kind of censorship online, and it's coming from the grassroots. Thanks to new collaborative, social media networks, it is easier than ever for people to get together and destroy freedom of expression. They are doing it DIY, from the bottom up, instead of top down the way old-school censors used to do it. Call it user-generated censorship.

Now that anyone with access to a computer and a network connection can post almost anything they want online for free, it's also increasingly the case that anyone with computer access and a few friends can remove anything they want online. And they do it using the exact same software tools.

Here's how it works. Let's say you're a community activist who has some pretty vehement opinions about your city government. So you go to Blogger.com, which is owned by Google, and create a free blog called Why the Municipal Government in Crappy City Sucks. But of course there are a bunch of people in Crappy City who disagree with you—maybe they even hate you personally. Instead of making mean comments on your blog, they decide to shut it down.

At the top of your Blogger blog, there is a little button that says, "Flag this blog." When somebody hits that button, it sends a message to Google that somebody thinks the content on your blog is "inappropriate" in some way. If you get enough flags, Google will shut down your blog. Ideally, this button is only used to flag illegal stuff or spam. But there's nothing to stop your enemies in town from getting together an online posse to flag your blog a bunch of times. Eventually, your blog will be flagged enough times that Google will take action.

And this is where things get interesting. Google has the option to simply shut down your access to the blog, but they rarely do that unless it's a situation where your blog is full of illegal content, like copyright-infringing videos. Generally, what Google will do if you get a lot of flags is make your blog impossible to find. Nobody will be able to find it if they search Blogger or Google. The only people who will find it, in fact, are people who already know about it and have the exact URL.

This is censorship, user-generated style. And it works because the only way to be seen in a giant network of user-generated content like Blogger (or MySpace or Flickr or any number of others) is to be searchable. If you want to get the word out about Crappy City online, you need for people searching Google for "Crappy City" to find your blog and learn about all the bad things going on there. What good is your free speech if nobody can find it?

Most sites that have user-generated content like photo-sharing site Flickr and video-sharing site YouTube use a system of flags similar to Blogger's that allows users to censor each other. Sometimes, you have to pick a good reason why you are flagging content—YouTube offers you a drop-down menu with about 20 choices—and sometimes you just flag it as "unsafe" or "inappropriate." And generally, most sites respond to flagging in the same way: they make stuff that's been flagged unsearchable, unfindable.

Censorship isn't working the old-fashioned way. Your videos and blogs aren't being removed. They're simply being hidden in the deluge of user-generated information. To be unsearchable, on the web, is in a very real sense to be censored. And you're not being censored by an authority from on high. You're being censored by the mob.

That's why I find myself rolling my eyes when I hear people getting excited about "the wisdom of crowds" and "crowdsourcing" and all that crap. Sure, crowds can be wise, and they can get a lot of work done. But they can also be destructive and cruel and stupid. They can prevent work from being done as easily as they can make it easier. And just as the web is making it easier for crowds to collaborate, the web is also making it simple for mobs to crush free expression.

Annalee Newitz is a surly media nerd whose blogs cannot be censored by the mob, even though she's well aware that there are mobs who would certainly like to do it.

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