VIDEO: How Iran's internet protesters slipped past censors

Despite attempts by Iran's government to block it, Twitter has become a crucial tool for Iranians to communicate.

They have been able to circumvent blocks and use the messaging site to spread news and plan protests.

"Iranelection" has been the most searched-for term on Twitter since unrest in the country began.

As Iranian authorities today launched a fresh crackdown on the site's use, Twitter users became involved in an electronic cat-and-mouse game to keep their connection to the service alive.

Iranians have been electronically disguising their whereabouts, creating a network of electronic "proxies" using dozens of different websites to post messages.

The government blocked access to Facebook and YouTube last week. But despite the move new videos of the protests were today being posted online.

As Mahmoud Ahmadinejad proclaimed his victory on Saturday, Iran's mobile phone network stopped working; text messaging in Iran remains blocked.

Professor Jonathan Zittrain of Harvard Law School said that Twitter was resilient to censorship because it had so many ways for users to post, such as computers and phones.

"The qualities that make Twitter seem inane are what make it powerful. With so many ways to get tweets there and back without the user needing twitter.com, it's far more censorship-resistant than other websites."

Government officials claim to be able to ban the keywords Twitter users use to mark their posts, such as #iranelection, causing confusion among users.

One message, posted early this morning from a user named fightforiran, said: "ALERT: #iranelection has been blocked in Iran.

Switch to #Iranians, #Tehran & #Iran9." But it was followed by a post claiming that the words were not being banned.

The Tweets were also being linked to YouTube videos and online news articles on Iran's disputed election result.

A steady stream of photos and witness reports have come from one Twitter user, persiankiwi, based in Tehran.

He has been forced to move location several times, and is also said to be orchestrating a campaign to bring down Iranian government sites by mobilising hackers around the world.

He wrote: "We honour and thank the people of Iran and especially the hackers Basij [the militia] have guns - we have brains."

Internet users in Iran have also used sites such as Flickr to post pictures of wounded or dead people who they say were protesters.