If I recall correctly, in Sweden the servers of political parties, served from their political offices, are immune to prosecution for a variety of offenses. It's intended to protect the freedom of independent parties. It just adds another layer of shielding on top of Sweden's other protections.
Not quite. Members of parliament there, as in many countries, have immunity from prosecution. But the Pirate Party is not, as of yet, represented in the Swedish parliament. There's a 4% of the popular-vote threshold for entry.
That said, Sweden has much more powerful transparency laws than most nations. Prior restraint on publication is banned, with the exception of cinema* and matters of national security. This can be challenged in court of course, like every democratic country they have due process. Every government document is public (per the constitution) unless explicitly classified, and has to be handed over, without question or delay. (E.g. anyone can waltz in to Rosenbad, the executive offices, and ask for a copy of the Prime Minister's e-mail from the last week). Classification requires explicit action (which again can be challenged in court) and is limited to national security, personal privacy, documents which are still under preparation, and a few other fairly obvious exceptions.
Source protection is exceptionally strong; If a classified document is leaked, it is illegal (unconstitutional, even) for the government to investigate, much less prosecute, the source of the leak. The only exceptions are essentially if the leak constitutes espionage or treason, or if it was an intentional violation of confidentiality (the latter is difficult to prove in court). In short, their government is severely limited in its powers to stop even its own leaks, much less leaks of information pertaining to foreign governments.
(* Cinema releases have to pass a ratings board that has the authority to cut footage or even ban releases. It's fairly inactive, today they only cut a few minutes of footage in total every year, almost exclusively for violence, not profanity or nudity. I believe the last movie that was banned from cinematic viewing altogether was the original Texas Chainsaw Massacre, 36 years ago)