Citing security, the agency has shut down an online network used by prisoners in secured facilities, newspaper Jyllands-Posten reports.
The secure network SK-net, which gives prisoners in some facilities online access, has been closed by the prison regulator, according to the report.
One consequence of the decision is the cancellation of online study programmes and exams.
The decision is reported to have been made in April after extremist material was found on four Playstation consoles at a secure prison in Nyborg.
Although the consoles were not directly connected to the internet, Kriminalforsorgen believed the material to have been transferred to them via USB drives.
But the decision will affect all inmates, not only those in danger of being radicalised, said Frederik Jepsen, a board member with charity Landsforeningen Krim, which offers legal support to prisoners in Denmark.
Caution should be taken with measures that can constitute collective punishment, despite the need to increase security against potential radicalisation, Jepsen said.
“Individual assessments of prisoners are required to assess whether the individual in question is suitable for access to the SK-net,” he told Jyllands-Posten.
Prisoners have been left disappointed that they are currently unable to continue education programmes, he added.
Lars Rau Brysting, head of security with Kriminalforsorgen, told Jyllands-Posten that the agency had long considered whether to continue using the SK-net, but that the discoveries on the Playstations had made an immediate decision necessary.