Hundreds of private photos from a number of female celebrities — including Jennifer Lawrence, soccer star Hope Solo, and Kim Kardashian — were posted by hackers to the messaging board 4chan over the weekend, in a repeat of a similar incident at the end of August. The hacks — besides being a horrible violation of the depicted celebrities' privacy and a minimization of their talent — are a reminder of the huge influence 4chan still wields more than a decade after its creation. All the same, the site's culture and history can be impenetrable to people who've never encountered it before. Here's a basic guide to one of the Internet's most infamous online communities.

1) What is 4chan?

4chan is, at root, nothing more than a collection of online forums of the kind that have existed in one form or another since the invention of the computerized bulletin board system in 1973. The site was created by Christopher Poole (better known by his username, moot), then a 15 year old high school student in the suburbs of New York City, on October 1, 2003. According to a profile by Fernando Alfonso at the Daily Dot, Poole had previously been active at Something Awful (SA), a comedy site whose forums, like 4chan, served as a breeding ground for new memes. A huge fan of anime, Poole also frequented the huge Japanese forum site 2channel ("2ch" for short) and its offshoot Futaba Channel ("2chan").

Out of a desire to, as Alfonso put it, "combine 2chan’s anime culture with SA’s dedicated community," Poole took Futaba's source code, translated the site text to English using Altavista's Babelfish translation tool, and named the result 4chan. He told the New York Times' Nick Bilton that he "wanted to keep with the 2chan naming and the URL for 3chan was taken at the time, so I just jumped to the next number." Poole still runs the site, at one point accumulating $20,000 in debt due to the cost of hosting it.

Unlike a lot of forum sites, 4chan doesn't have user registration — everyone's postings are entirely anonymous, or use a pseudonym chosen on the spot. And unlike a traditional bulletin board or community moderated sites like Reddit or Hacker News, posts are ordered reverse chronologically, as on a blog.

2) How popular is 4chan?

4chan claims to have 20 million unique visitors and 540 million page views a month. According to Alexa, it's the 461st most popular website in the United States and the 974th most popular one in the world. Those are really impressive figures, but it's less popular than some similar sites, most notably Reddit, which is the 18th most popular site in the US and 50th worldwide, and as of July 2014 claimed almost 115 million unique visitors and over 5 billion page views over the previous month.

3) What is /b/?

In the beginning, 4chan had only two boards: /a/, for anime discussion, and /b/, for everything else. The site has many more these days, but /b/ remains the most popular and the epicenter of the culture that has come to be associated with the site; it's because of /b/ that 4chan gets dubbed things like, as Tim Lee put it, the "Mos Eisely cantina of the Internet." "Measured in terms of depravity, insularity and traffic-driven turnover, the culture of /b/ has little precedent," Matthias Schwartz wrote in the New York Times Magazine. "/b/ reads like the inside of a high-school bathroom stall, or an obscene telephone party line, or a blog with no posts and all comments filled with slang that you are too old to understand."

At its most benign, /b/ helps generate memes that become an ingrained part of web culture. LOLCats, for example, are generally traced to Caturday, a weekly tradition wherein users posted cat pictures on the board. Rage comics originated on /b/ too. But the board's users also have a history of harassment and bullying. Schwartz notes a particularly bad case, in which /b/ users (or "/b/tards," as they are sometimes known) took the case of a real seventh grade who committed suicide, embellished it with made-up details (principally, that he had killed himself over a lost iPod), and took to doing things like photographing his grave with an iPod next to it, or prank-calling his grieving parents. In another case, they repeatedly harassed a 11-year-old girl who complained about the board on her video blog.

4) I feel like I'm entering a terrifying nightmare world. Can we have a music break?

Of course. Perhaps the most popular and enduring 4chan-originating meme (birthed on its /v/ video game board, not /b/) is the Rickroll, wherein the rickroller tricks the rickrollee into watching the music video of Rick Astley's "Never Gonna Give You Up." This section is an extremely poor Rickroll since I'm telling you it's about to happen:

5) What are some basics of 4chan I should know?

4chan's culture is intricate and ever-evolving, but some key things you should know include:

Encyclopedia Dramatica which, in addition to serving as a sort of 4chan version of Wikipedia, archiving memes and stories and operations undertaken against various targets, has become a kind of community of its own.

which, in addition to serving as a sort of 4chan version of Wikipedia, archiving memes and stories and operations undertaken against various targets, has become a kind of community of its own. Pedobear , a 4chan-originating meme of a cute-looking bear which, the joke goes, is a mascot for pedophiles.

, a 4chan-originating meme of a cute-looking bear which, the joke goes, is a mascot for pedophiles. Poll hacking, a common 4chan pastime, most famously used against TIME Magazine in a poll to determine readers' choice for most influential person of 2008. 4chan succeeded in winning the poll for its founder, moot. In another case, they gamed a contest to force rapper Pitbull to do a show in Kodiak, Alaska.

Google pranking, in which users search for agreed-upon terms in an attempt to have them "trend" on Google. Searches that have topped the trending list, at 4chan's instigation, include a swastika and the phrase "lol n-----rs."

Hoax hashtags, in which 4chan users attempt to get Twitter users to seriously use hashtags invented to troll them. The most recent one was #leakforjlaw, which attempted to persuade women to post their own private nude photos in solidarity with Jennifer Lawrence, but arguably the most vile was #cuttingforbieber, which tried to get Justin Bieber fans to engage in self-harm.

News hoaxes, such as one in October 2008 that claimed that Steve Jobs had died and sent Apple stock plummeting.

Email hacks, notable targets of whom have included Sarah Palin and the late Trayvon Martin.

Misogyny and racism, which are persistent problems in the 4chan community, especially on /b/, though many users claim they use racial slurs and the like in an attempt to provoke rather than out of malice.

6) Is 4chan the same thing as Anonymous?

Not exactly, no, but the very loosely organized political activist/vigilante group that has come to be known as Anonymous originated on the 4chan boards. As Quinn Norton recounted in her history of Anonymous for Wired, the group grew out of a tradition of "raids" by /b/ users. "Raids," in this sense, involved using "the technological tools of social coordination so quickly and well that anons working together could collectively attack targets for any perceived slight, or just for fun, without those targets ever having a chance to see it coming or defend themselves," as Norton puts it. "Doxing [publicly releasing sensitive information about people], ordering unpaid pizzas, signing people up for embarrassing junk mail were all common raids."

Some of these early raids had a moral element, such as bringing abusers of cats to police attention, but the first major Anonymous campaign came in early 2008, when the Church of Scientology tried to force Gawker to take down a video of Tom Cruise singing the church's praises. The result was Project Chanology, wherein Anonymous targeted Scientology first with things like dedicated denial of service attacks and then, starting on February 10th, protests and other nonviolent, legal means of resistance, often employing Guy Fawkes masks (from the graphic novel and film V for Vendetta) as a trademark.

Eventually Anonymous outgrew 4chan and became a force of its own, organizing on other fora such as IRC chat channels in addition to /b/. Other targets have included police involved in cracking down on Occupy Wall Street, child porn networks, credit card companies and other financial companies which refused to work with Wikileaks, and the Steubenville, Ohio rapists. Notably, the group also targeted the revenge porn site Is Anyone Up?, which underscores why it's important to differentiate the 4chan users involved in the celebrity photo leak from other users who have taken strong stands against posting peoples' nude photos without permission.

7) Were other sites involved in the celebrity photo leak?

Yep. Reddit has also been responsible for propagating the photos, with a subreddit known as "theFappening" serving as ground zero until it was shut down by site administrators. In its wake, however, other subreddits have emerged to distribute the photos (we won't link to them here and you shouldn't visit them).

Jordan Sargent at Gawker reports that it appears the first wave of hacks got going not on 4chan or Reddit but on AnonIB, a breakaway forum site which began "after a mutiny temporarily splintered 4chan's infamous /b/ board" that "focuses more or less exclusively on pornography—in particular, stolen or leaked nudes of non-celebrity women."

The FBI has been investigating the hacks since early September, and actress Gabrielle Union, a victim of the latest round, has asked the bureau to intervene again. But there have been no signs that the perpetrators are close to be identified or apprehended.

This post has been updated to reflect the second round of hacked photo leaks that occurred the weekend of September 20, 2014.