Hackers belonging to the Anonymous collective have brought down more than 300 websites operated by Thai courts over the British backpacker murders verdict. The websites were hacked in protest after a court sentenced Myanmar migrants Zaw Lin and Win Zaw Tun to death.

"Anonymous shuts down all Thai Court of Justice websites in protest over the Koh Tao murder verdict. Anonymous is supporting the campaign to ask tourists to boycott Thailand until such time that changes are made with the way Thai police handle investigations involving foreign tourists" the hackivists said in a Facebook post.

The group had earlier paralysed Thai police websites after the verdict was announced. The duo from Myanmar were held guilty of the murder of British tourists Hannah Witheridge, 23, and David Miller, 24.

The judgement has been fiercely contested by critics who say the confessions by the two Myanmar migrants were extracted through torture. Police officers are also accused of carrying out a botched investigation and mishandling DNA evidence.

The British victims were found dead on a beach on the resort island of Koh Tao in September 2014. Witheridge was found raped before her death.

Responding to the latest cyberattack, Suebpong Sripongkul, spokesperson for the Courts of Justice in the country, said: "The hackers' attack cannot change the lower court's verdict, but both sides can appeal to higher courts." He said there would legal action against the hackers.

Anonymous – a loosely-organised group of activist hackers, or hackivists – has also threatened to release confidential data exposing alleged corruption of Thai officials. Though Thai officials have confirmed several pages of Thai websites have been down they have insisted no information was stolen. "They're not good enough to hack into our system and steal any of our data," police spokesperson Dechnarong Suthicharnbancha told Reuters.