If Facebook didn't start the Arab Spring it certainly helped accelerate the uprisings.

Now the social network's role in toppling regimes has catapulted Mark Zuckerberg into the Forbes list of the 10 most powerful people on the planet.

The Facebook founder, 27, is the fastest riser in the business magazine's annual ranking of the "70 Most Powerful People In The World", soaring from number 40 to nine.

President Barack Obama returns to the top of the list, displacing Chinese President Hu Jintao, who also falls behind Vladimir Putin, the Russian Prime Minister.

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The phone-hacking scandal has taken the lustre off two notables. British Prime Minister David Cameron falls three to number 10, with Forbes citing his links with Andy Coulson, the No 10 communications director who quit after claims that he knew about hacking when editor of the News of the World.

Forbes wrote: "Once hailed as the second coming of Margaret Thatcher, [he] now serves as the UK's punching bag." Rupert Murdoch, the News Corporation CEO, who closed down the News of the World and saw his bid to control all of BSkyB collapse, tumbles down the list from 13 to 24.

New entries include Wen Jiabao, the Chinese Premier at 14, Opec president Rostam Ghasemi at 32, and Christine Lagarde, the new IMF managing director at 39. Lagarde's predecessor Dominique Strauss-Kahn, who resigned amid sexual assault charges, drops out of the list, with Julian Assange and Oprah Winfrey.

The Forbes panel assessed four factors: how many people they have power over; the financial resources they control; if they have influence in more than one sphere; and how actively they wield their power to change the world.

Zuckerberg, worth US$17.5 billion ($22.4 billion), is following the example of Bill Gates, giving US$100 million to improve US schools. Gates is at number five.

Two criminals made it: Joaquin Guzman Loeran, 55, head of a Mexican drug cartel, and Dawood Ibrahim Kaskar, 57, head of a Mumbai crime syndicate.

- Independent