French TV5Monde television channel, which suffered a major hack by self-proclaimed Islamic State militants this week, on Friday admitted an Internet security 'blunder' Thursday during a programme discussing the cyber-attack.

The gaffe came during a report by fellow TV channel France 2 on the attack on TV5Monde, which authorities say was likely a "terrorist act".

A TV5 Monde journalist being questioned was in front of a window where several sheets of paper were hanging. On one of them could be seen a password for the TV5Monde YouTube account.

"We don't hide the fact that this is a blunder," the channel's director general Yves Bigot told AFP.

However he stressed that the codes were displayed on screen only after the cyber-attack which happened overnight Wednesday when hackers managed to shut down transmissions and hijacked the channel's website and social networks.

TV5 Monde's digital services director Helene Zemmour explained that after the hacking attack the channel had needed to quickly hand out new temporary online access codes.