Last updated: 10 february, 2010 - 15:28 GMT
Iran's cyber-war on Twitter
Twitter was one of the ways protesters shared information with the outside world
Thursday 11 February 2010 is the 31st anniversary of Iran's Islamic revolution and it already looks as though it is going to be a major day of protests.
Government supporters and opponents are being called on to take to the streets.
News of the opposition protests will probably come via the web, from an army of citizen journalists.
Since the disputed presidential election in June last year, the role of social media in Iran has been evolving fast.
The BBC's Tehran correspondent, Jon Leyne , who was expelled from Iran after the election, reports from London.
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First broadcast 10 February 2010
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