Several official Swedish websites were knocked offline for several hours on Monday, although no group has claimed responsibility for the attacks.
The websites of the Swedish government, Armed Forces and the Swedish Institute were among those experiencing problems.
"I can confirm that the government site had problems today, but for security reasons, I cannot say more," Anna Dahlen, a government spokeswoman, told the AFP news agency adding that she did not know when the site would be back online.
Among websites hit were sweden.se - which gives general information about the country, and studyinsweden.se.
Patrik Braennstroem, web host of sweden.se, said it "came under a DDoS [distributed denial of service] attack".
He believes that other official sites were "undoubtedly" victims of the same attack.
Niklas Englund, head of digital media at the Swedish Armed Forces, said it was unclear who was behind the so-called DDoS attacks, in which websites are overwhelmed with bogus traffic.
But he noted that an unidentified group urging Sweden to take its "hands off Assange" claimed responsibility on Twitter.
WikiLeaks founder Julian Assange has been sheltering at Ecuador's Embassy in Britain since June 19 in an effort to avoid extradition to Sweden, where prosecutors want to question the founder of the whistleblower website WikiLeaks over alleged sex crimes.
Meanwhile, a tweet by he Swedish branch of Anonymous hackers said: "There were claims last night about regeringen.se being hit, but we really can't confirm it at this stage," referring to the government's website.
Anonymous "usually claims its attacks and does it noisily," Internet community expert Marcin de Kaminski told AFP.
Anonymous has carried out several cyber attacks against government websites, including those of Poland and Greece.