The teens, who said they were all 16, admitted to the hacks in a statement posted on a site, TheLocal.se reported.
The attackers are believed to have used direct denial-of-service attacks against government and transportation websites, overloading them and causing them to crash.
A site that offers online ticket sales for a government-owned railway was hacked, making it impossible for travelers to purchase tickets. Other hacked sites included a retail alcohol company and a regional public health system.
A spokesman for the Malmo police, Lars Forstell, declined to comment on the teens' claims but said the hacks represented "serious criminal activity."
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