A year after e-mailed images of its brutal crackdown against democracy demonstrations were transmitted across the world, Burma has launched a ferocious “cyber-war” against dissidents who use the internet.

In the past few days anti-government online magazines run by exiled Burmese have been inundated by massive volumes of artificially generated traffic that have forced the news websites to shut down. The attacks coincided with the first anniversary of the “saffron uprising” — ten days of mass demonstrations by Buddhist monks and student activists that culminated in a crackdown in which dozens were killed and thousands arrested.

The concerted attacks - which appear to originate in China, Russia and Europe as well as Burma — can only be the work of agents of the Burmese Government and may be an effort to compensate for its failure last year to stem the flow of images showing vast columns of unarmed demonstrators and their eventual dispersal under a rain of bullets and truncheons.

Aung Zaw, editor of The Irrawaddy magazine and news website, based in the Thai city of Chiang Mai, said: “This attack is revenge. Last year the people beat the Government in the cyber-wars by getting lots of images and live news reporting out. Now the Government is saying, ‘We're much more advanced than before and we can cripple you'.”

The attacks began last Wednesday when three websites — The Irrawaddy, the Oslo-based Democratic Voice of Burma and the New Era in Bangkok — became inaccessible. Within hours, the internet service providers for The Irrawaddy's main site and its back-up site were forced to shut them down.

The attacks were of the type known as distributed denial-of-service, which use automated programs to simulate thousands of users accessing the site simultaneously, overloading it.

The attacks eased over the weekend but Mr Aung Zaw said he feared that they would resume this week in the build-up to the anniversary of September 26, 2007, when the Government imposed a curfew and began its attacks and arrests on demonstrators.

Although only three websites have been affected they have a disproportionately large influence in reporting in a country where domestic media are strictly censored and foreign journalists can work only clandestinely.

The Irrawaddy, the most popular of the news services, has correspondents working undercover in Burma and on the Thai border. The print version has only 400 subscriptions but its website has 25 million hits and 100,000 unique visitors a month, including diplomats, journalists and activists following Burma.

A year ago the junta was shamed by the images of the saffron uprising and seemed helpless to prevent them. Eventually it shut down the internet for four days but by that time pictures had been broadcast across the world, including the notorious film of Kenji Nagai, the Japanese photographer, shot dead by a Burmese soldier.

The latest cyber-retaliation suggests that General Than Shwe, the junta's septuagenarian leader, has learnt lessons and is prepared to go on the offensive. Mr Aung Zaw said: “It's easy to see the generals as dinosaurs but they are not stupid. They have a lot of sophisticated, well-trained people - although you wouldn't think it to look at Than Shwe.”