A French television network has been hacked by people claiming allegiance to the Islamic State group.
The hackers briefly cut transmission of 11 channels belonging to TV5 Monde and took over its websites and social media accounts.
The channel's director, Yves Bigot, said this morning that the attack was continuing. He told RTL radio that the network has restored its signal but can only broadcast recorded programmes.
The message on the TV5 Monde website read in part "I am IS" with a banner by a group that called itself Cybercaliphate.
The Islamic extremist group has claimed complex hackings before but the seizure of the French network appeared to be a new step in its information warfare tactics.
The Paris prosecutor's office said it has opened an investigation into the attack.
Mr Bigot said he was shaken when he saw the black screen across the network's broadcasts "and when we discovered the sense of the message appearing on our social media and our websites, it both allowed us to understand what was happening and obviously worried us".
In a Facebook message that went up after the network resumed control of the site, Mr Bigot said the "very powerful cyber attack" began on Wednesday at 10pm.
Prime minister Manuel Valls, on his Twitter account, called the attack "an unacceptable insult to freedom of information and expression" and expressed his support for the editorial staff. Interior minister Bernard Cazeneuve, foreign minister Laurent Fabius and culture minister Fleur Pellerin visited the channel's Paris headquarters.
TV5 Monde, which was founded by the French government in 1984 and calls itself the "worldwide French cultural channel", broadcasts programmes produced in France, Belgium, Switzerland and Canada, as well as films, news and other programmes. Its Facebook page says its signal reaches more than 257 million homes in over 200 countries and territories.
After January terrorist attacks in France by gunmen claiming links to IS and al Qaida in Yemen, officials said hackers had targeted some 19,000 French websites. William Reymond, editor of the French investigative website Breaking3zero, which traced the January hackings, said the latest attack can be directly linked to two IS-linked militants - one in Algeria who built the malicious software and another in Iraq who helped speed up the attack.
Within half an hour, he said, the malware had burrowed in and exploited a weakness to enter the network's computer system and take over its central transmission server, which translates an analogue signal into a digital one before it is beamed to a satellite. He said TV5 Monde will have a hard time regaining full control.
"They have to erase everything. There were at least three other encrypted viruses," he said.
IS has called out France in particular for attacks, but Mr Reymond could not say whether they had a particular reason to target TV5 Monde.
A French security official said investigators would examine whether the attackers had found a hole in TV5 Monde's information defence systems that was left unguarded, or whether those systems failed outright, which he said would be a more worrying development.