"We have had hacker attacks over the past 24 hours. We have no idea where it is coming from," Sweden Democrats spokesman Erik Almqvist told AFP, adding that the party expected to get its website running again soon.
When AFP viewed the site early Saturday afternoon, only a digitalised picture made up of numerals to look like a piece of birthday cake with a lit candle was visible.
Below the picture, a short text read: "Anyway, this cake is great. It's so delicious and moist. Look at me still talking when there's Science to do," as Ellen McLain's "Still Alive" played in the background.
"I think it is a shame. Our political opponents should take the debate with us if they disagree with us," Almqvist said, insisting the attack "doesn't do any good for democracy."
The hacker attack came on the eve of general elections, with polls hinting the Sweden Democrats for the first time will win more than the four percent needed to enter parliament.
The far-right party, which won just 2.9 percent of the vote in the 2006 elections, has been seen winning as much as 7.5 percent on Sunday, although three polls published Saturday handed it between 3.8 and 5.9 percent of voter intentions.
The surveys meanwhile showed the centre-right government's lead over the left-wing opposition shrinking slightly but still winning a narrow majority in parliament.
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If neither side wins a clear majority, however, the Sweden Democrats could, even with just a handful of seats, play kingmaker and could even make it so difficult to govern that new elections would need to be called, observers say.