Julian Assange is wanted in Sweden to face questioning over rape and molestation accusations, and many activists say that this prosecution is part of USA-led attempts to stop Assange and the Wikileaks whistleblowing website.
Hospitals from the Västra Götaland region, which includes the city of Gothenburg, were hacked in August. The local head of IT, Göran Ejbyfeldt, says to news agency TT that the attack was kept quiet, in an attempt to minimise the damage. During the hack a video supporting Julian Assange was uploaded to one of the Västra Götaland region's websites.
A hotline for worried patients has now been set up, after the story was revealed in the tabloid Expressen on Friday.
The hackers would have been able to see name, identity number and diagnosis for patients from the early 1990s to 2009.
The matter has been reported to the police.