4chan is the website where the stolen images of more than 100 nude celebrities - including photos of Jennifer Lawrence, Kirsten Dunst and Kate Upton - were first widely shared.
It's the birthplace of some of the internet's most familiar memes, such as Rickrolling and LOLcats.
And an anonymous space where users can post everything from physics problems to hardcore porn.
We spoke to two experts and a regular user to create a guide for the perplexed.
What is 4chan?
In its own words, "4chan is a simple image-based bulletin board where anyone can post comments and share images."
There are boards dedicated to topics such as music, fashion, fitness, video games and science.
But the most notorious board - and one of the most popular - is "random" or "/b/", which features graphic imagery of sex and violence.
"It's absolute grotesque chaos," says 24-year-old student and long-time user Alex, who asked us not to use his last name. "/b/ is very different from some of the purpose built boards, such as music or video games or world news."
Tama Leaver, a lecturer in internet cultures at Curtin University, called /b/ "an irreverent image board that goes out of its way to shock".
How did it begin?
In 2003, Christopher Poole created 4chan as a site devoted to Japanese anime and manga pictures. He was in his early teens.
In 2009, the New York entrepreneur was voted the world's most influential person in an online poll by Time magazine, a ballot which many speculate was rigged by 4chan users.
Who uses 4chan?
Anyone can use the site as it requires no registration. Most eschew a user name, preferring to post as "anonymous".
"The whole principle of 4chan and its anonymity goes back to a perceived golden age of the internet, prior to Facebook, prior to social media," says Steve Collins, a Macquarie University media lecturer.
Leaver says the site is mainly used by a "young, male, affluent, western, demographic".
Alex believes many young male teenagers are drawn to an anarchic, "anything goes" spirit of 4chan.
Women are not welcome on the /b/ board. Those who identify as girls or women are told "tits or gtfo" - "post an image showing your breasts or get the f--- out".
What are the rules?
Officially, there are 17 "global rules" that apply across the site. They include observance all United States laws and a requirement that users are over 18 years old, as well as housekeeping dictums about posting in the right boards.
But /b/ is almost entirely lawless. A prohibition of child pornography is perhaps the sole rule which is generally observed.
Are the rules enforced?
Leaver says 4Chan generally complies with requests from law enforcement bodies, and has a team of volunteer moderators enforcing rules, where they exist. But the nature of the site means offending content often disappears off the main site long before it can be formally tackled.
What is it like?
Student user Alex finds many of the boards useful.
"Fashion has really great lists of websites and discounts that are going on," he says.
But on /b/, it is a very different story.
Collins says there are "a lot of posts around girls and sex, like 'Facebook friends I would like to f---'."
"There's also quite a lot of explicit racism and a lot of nationalism in there."
Then again, Collins says he finds humorous and sometimes insightful messages amidst the degrading material.
Leaver refers to the site's political activity, including the targeting of corrupt Chinese politicians.
"It's a bit like the court jester's role in that you can say things that other people can't say," he says.
How does 4chan relate to the Anonymous group?
4chan is said to have spawned the online hacker group Anonymous, which has targeted major companies such as PayPal, churches such as Scientology, and even the US government. But 4chan and Anonymous are now independent, even if there is some cross-over in membership, according to Collins.
4chan and /b/ glossary
btards - users of the random message board, /b/
new fags, old fags - new and old users
OP - original post, original poster
OC - original content
cancer - old, irrelevant, or boring content
moot - creator Christopher Poole's nickname on the site
