Internet attacks blocked access to several popular Swedish websites for part of Monday, local police said, linking the outage to the controversy surrounding WikiLeaks founder Julian Assange.
"Every time something happens in the Assange affair there are more attacks on the Internet in Sweden," a national police computer expert, Anders Ahlqvist, told AFP.
The Australian activist, 41, has been holed up in the Ecuadoran embassy in London since claiming asylum on June 19 in a bid to avoid extradition to Sweden, where he faces questioning over alleged sex crimes.
Assange denies the allegations and says he fears Sweden would extradite him to the United States, which was deeply embarrassed by WikiLeaks' release in 2010 of huge caches of US diplomatic cables and confidential documents on the wars in Iraq and Afghanistan.
Assange supporters claim he could receive harsh treatment if sent to the US and possibly even face the death penalty.
The Swedish authorities want to question him over allegations of rape made by two Swedish women.
Ahlqvist said it was obvious that the number of Internet attacks aimed at Sweden had increased since the case against Assange had emerged in 2010, even if it was hard to establish a formal link.
"As long as the Assange affair continues we shall see attacks on Swedish targets," he said.
"I have the impression that an inventory of the state of security of the websites of major Swedish businesses is being drawn up."
The sites of major banks, such as SEB and Swedbank, were hit Monday, as were those of the national railway company SJ and the TT news agency.
Complaints were filed during the day but have not been centralised, Ahlqvist said, refusing to say whether police had specific evidence pointing to pro-Assange groups.
Monday afternoon there had been no claims of responsibility for the attacks.
On September 3 the websites of several Swedish public authorities, including that of the government, were paralysed by a DDoS (distributed denial of service) attack, in which sites are overwhelmed by a deluge of requests, putting them out of service.
A pro-Assange group said it was responsible.