The importance of social media is perhaps best illustrated by the government's response to it. Many sites have been filtered or blocked in Iran, including YouTube and Facebook. The speed of the internet was also deliberately slowed down. And Prominent bloggers, like the former vice-president Mohammad Ali Abtahi, were among those first arrested. More recently the so-called Iranian cyber army has attacked reformist websites, and the organisers have had their computer files deleted.
via guardian.co.uk