The Nobel Peace Prize website came under cyber attack from Taiwan, Norwegian telecoms operator Telenor said Tuesday, less than three weeks after jailed Chinese dissent Liu Xiaobo won the award.

"The site was compromised, or as is more commonly said, hacked," Frank Stien, in charge of computer security at Telenor told AFP, confirming a report in the Aftenposten daily.

Visitors to the website risked infection by a "Trojan horse" virus, a difficult to detect programme that allows hackers to take control of victims' computers.

Stien said the last IP address used by the hacker was at the National Chiao Tung University in Taiwan, but he cautioned that the attack may have originated elsewhere as hackers often used many computers to hide their traces.

"We cannot say anything about the identity of the hacker or his motivations," Stien said.

The Nobel Institute in Oslo said it had heard of the attack but said the site was now back to normal.

"It is no longer dangerous to visit the website, the problem has been solved," Sigrid Langebrekke at the institute said, refusing to comment further.

Liu Xiaobo, a 54-year-old former university professor, was awarded the Nobel Peace Prize on October 8, angering China which has since voiced its discontent to Norway.

Liu was jailed in December for 11 years on subversion charges after co-authoring Charter 08, a bold manifesto calling for political reform in one-party Communist-ruled China. Beijing considers him a criminal.