Few terms you need to know before proceeding.
Anonymous - An unidentified individuals posting on chatrooms , forums etc.
4Chan - An English-language imageboard website.
Imageboard - A type of Internet forum that revolves around the posting of images.
Trolls - Someone who posts inflammatory, extraneous, or off-topic messages in an online community,
Ok, lets get started. 4Chan started in October 1 2003 as a source for the western side of the earth to share their love for Japanese culture (Anime manga and such) . Most users post anonymously and many are professionals in their own way . There are lawyers, doctors, artist, teachers and etc using 4chan anonymously.Internet memes are made and popularize in 4Chan, specifically the /b/ board.
People on /b/ board are mostly trolls. 4Chans are also responsible for many protest against governments of different countries, and the most well known would be their fight against the religion, Scientology.
On Jan 2008, Tom Cruise gave an interview on how great Scientology is, and it sparks off a massive reaction from the Anons in 4chan.The Anon leaders (who are Anon themselves) started Project Chanology. The video of the interview has been taken down by youtube so i cannot show you guys the video , sorry !
Below is the video the 4Chan's anons sent out to the churches of Scientology.
The video says :
Hello, Scientology. We are Anonymous.
Over the years, we have been watching you. Your campaigns of misinformation; suppression of dissent; your litigious nature, all of these things have caught our eye. With the leakage of your latest propaganda video into mainstream circulation, the extent of your malign influence over those who trust you, who call you leader, has been made clear to us. Anonymous has therefore decided that your organization should be destroyed. For the good of your followers, for the good of mankind--for the laughs--we shall expel you from the Internet and systematically dismantle the Church of Scientology in its present form. We acknowledge you as a serious opponent, and we are prepared for a long, long campaign. You will not prevail forever against the angry masses of the body politic. Your methods, hypocrisy, and the artlessness of your organization have sounded its death knell.
You cannot hide; we are everywhere.
We cannot die; we are forever. We're getting bigger every day--and solely by the force of our ideas, malicious and hostile as they often are. If you want another name for your opponent, then call us Legion, for we are many.
Yet for all that we are not as monstrous as you are; still our methods are a parallel to your own. Doubtless you will use the Anon's actions as an example of the persecution you have so long warned your followers would come; this is acceptable. In fact, it is encouraged. We are your SPs.
Gradually as we merge our pulse with that of your "Church", the suppression of your followers will become increasingly difficult to maintain. Believers will wake, and see that salvation has no price. They will know that the stress, the frustration that they feel is not something that may be blamed upon Anonymous. No--they will see that it stems from a source far closer to each. Yes, we are SPs. But the sum of suppression we could ever muster is eclipsed by that of the RTC.
Knowledge is free.
We are Anonymous.
We are Legion.
We do not forgive.
We do not forget.
Expect us.
It became so serious and wellknown in the 4Chan world that Anons all over the world starts rioting against Scientology. Donning the mask of Guy-Fawkes ( A hero in the 1590s' ) , they start protesting about Scientology. Websites regarding Scientology was also hacked by the Anons.
More information can be found here : wiki
I will end this post here with you thinking about this picture.

Is 4Chan be a threat, or a blessing to mankind?
Links:
4Chan
2chan(The first imageboard in the world)
Scientology
Warning , enter 4chan at your own risk.
Gawker, a popular blog based on New York states that"reading /b/ will melt your brain" .