As protesters continue to clash with police on the streets of Iran, the backlash over the country's controversial election has taken to the web.

Supporters of reformist candidate Mir Hossein Mousavi have taken to the streets in huge numbers to protest against the re-election of president Mahmoud Ahmadinejad amid widespread allegations of fraud and tampering with election results.

While protesters take to the streets, both sides of the election are believed to be taking the fight to the web with hack attacks.

A number of people have used micro-blogging service Twitter and other blogs to direct users to a number of sites and tools which are being used to cause distributed denial-of-service attacks against government web sites.

The Iranian government and its supporters are also said to be taking to the web. A number of sites reporting news of the protests, including that of The Atlantic magazine writer Andrew Sullivan, are said to be the target of denial-of-service attacks themselves.

The use of web attacks to coincide with physical conflicts has become more common in recent years. Hackers in Russia and Eastern Europe have been particularly active on the web in such conflicts as those in Georgia and Estonia.

The attacks primarily target government infrastructure sites and news sites as a way to cut off an opponent's ability to communicate over the web.

In 2007, government officials in Burma opted to cut all internet access in the country in an effort to prevent the posting of videos and photos of violent clashes amid a series of pro-democracy protests.