Repressive governments are arresting more bloggers than ever as they struggle to cope with the threat posed by the internet, researchers have claimed.

Thirty six people were arrested last year because of what they had written on their blogs and personal websites – an increase of more than three times on the figures from 2006, according to researchers at the University of Washington in the US.

The latest edition of the annual World Information Access report says that there has been a significant increase in those falling foul of the law in countries such as China, Egypt and Burma.

"Egypt, Iran and China are the most dangerous places to blog about political life, accounting for more than half of all arrests since blogging became big," said Phil Howard, an assistant professor of communication at the university.

He believes that the figure of 36 may be a dramatic underestimate, because many arrests are never made public.

"The real number of arrested bloggers is probably much higher, since many arrests in China, Zimbabwe and Iran go unreported in the international media," he said.

Blogs have become massively popular way for people in countries with authoritarian regimes to express themselves, and part of the increase could be explained by this growing popularity – there are estimated to be more than 70 million such websites in China alone.

But the fact that governments are paying increasing attention to what people say about them online means that it is becoming more dangerous for those who choose to write about their life on the web.

While the reasons for the arrests vary from place to place, the most common transgression involves organising a social protest. This was the reason given for five of Egypt's record nine arrests in 2007, as well as incidents in Burma, China and Iran.

While not all those arrested because of their blogs were imprisoned, the report says that the average sentence for those who were sent to jail was 15 months.

However, the numbers so far in 2008 seem significantly lower, with just five bloggers having been arrested around the world during the first quarter of the year - including Welshman Gavin Brent, who was convicted in April of writing "grossly offensive and menacing messages" on his site.

Another of those arrested so far this year Burmese blogger Nay Phone Latt, who disappeared in January before it emerged that he had been charged under the country's notorious Emergency Provision Act, which has been used to silence a number of dissidents since the anti-government protests last year.