Nobody would know the detail information of when Anonymous started activities.
There are many incidents that Anonymous has an opportunity to become famous.
But, the first momentum which made Anonymous famous is the “war” against Los Zetas.
Los Zetas is a Mexican mafia which is famous for smuggling drugs and weapons.
Especially, they retaliate brutally to their enemies or the people who slandering them.
(So, I do not recommend you to searching about Los Zetas on Google, it would be cruel.)
Just like other days, Los Zetas kidnapped all of the people who were in the Mexican pub to catch their enemy mafia members.
Suddenly, someone contact to a executive member of Zetas.
“You guys kidnapped a member of Anonymous. If you guys do not release him, we will publish Zetas’ irregularities and the current location of executives.”
Of course, he just laughed first.
But after one hour, a member of Anonymous was released due to a piece of fax which Anonymous send to Zetas’ hideout where ordinary people would not know absolutely.
There was all the information about Zetas’ irregularities and the current location of executives, even their siblings’ location.
(Anonymous Hacker Group Threatens Mexico’s Zetas Drug Cartel)
Zetas was super famous at this time. So after this incident published, Anonymous became famous.
I want to say that this incident made the awareness of today’s Anonymous.
There are some major actions of Anonymous.
1. There was an internet site which called “Megaupload”. People could share their files.
But American government removed this site, because it is a violation of copyright law.
So, Anonymous declared “cyber war” to government. They said it is the repression of information sharing.
(internet sites which Anonymous attacked)
Anonymous knock downed several major internet sites.
2. Anonymous declared war against Syria government
Because Syria government shut down the internet which is the place of communication today.
3. Protest about Aaron Swartz’s suicide
Anonymous hacked the machinery law of America and suggesting the possibility of a spill classified document.
But Anonymous did not revealed it, they just gave pin key to decode password.
Anonymous warned them.
I posted three major incidents, but they achieved more (You may easily find on Google)
I want to say mass media can really change (or affect) the world.