Gottfrid Warg, co-founder of the Swedish file-sharing website The Pirate Bay, was sentenced on Friday to three and a half years in prison.
Warg was found guilty of hacking into the mainframe of IT provider CSC in Denmark, accessing the Danish Civil Registration System and local police's criminal register in 2012.
The Court of Frederiksberg in Copenhagen said "the attack was systematic, intensive and took place over a long period of time," and that "significant amounts of highly sensitive personal information had been downloaded in the hacking campaign."
Warg has been in pre-trial detention in Denmark since November 2013, when he was extradited from Sweden after serving a jail sentence there.
In Sweden Warg had been convicted of copyright theft due to his involvement in The Private Bay, and separately for hacking the mainframe of IT consulting firm Logica.