Swedish government websites were jammed by hackers for hours on Monday, with some supporters of WikiLeaks founder Julian Assange claiming responsibility on Twitter.
The websites of the Swedish government, Armed Forces and the Swedish Institute were among those experiencing problems.
Niklas Englund, head of digital media at the Swedish Armed Forces, said it was unclear who was behind the so-called denial-of-service 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.
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 secret-spilling WikiLeaks site over alleged sex crimes.