The Pirate Bay co-founder Gottfrid Svartholm Warg was banged up for three and a half years on Friday.
The jail term comes after the 30-year-old was found guilty of hacking charges by a court in Denmark on Thursday.
Warg and an unnamed, 21-year-old accomplice hacked into the mainframe of American tech outfit CSC, which was hosting European government organisations between February and August 2012.
They then proceeded to illegally access police email accounts, searched the European border control database and downloaded millions of social security numbers belonging to Danish citizens, Frederiksberg court heard earlier this week.
Warg, who has been in pre-trial detention in Denmark since November 2013, is expected to appeal against his sentence according to Swedish news site The Local.
His accomplice was handed six months in the slammer, Reuters reported, but he walked free from court having already served 17 months in pre-trial detention. ®