Police say hundreds of pornographic pictures of children have been available on a free website provided by Microsoft's MSN service.
The Swedish-language website was on a US-based server that was shut down on Friday after police alerted Microsoft officials in Sweden.
Lars Backhans, Nordic director for MSN, says: "We have zero tolerance for this. Personally, I find it downright disgusting. We are doing all we can to assist the police in their investigation."
The website was offered on one of Microsoft's Web Communities, which the company describes as "free websites that are created and maintained by other users".
Backhans says there are 12,000 to 13,000 such websites in Sweden alone, making it virtually impossible for Microsoft to monitor their content.
However, he says each subscriber must agree to contract terms that ban illegal material such as child pornography.
Police Superintendent Tommy Moork, of Oerebro, about 85 miles (140km) west of Stockholm, says: "Each time these pictures are shown on the internet, it's as if the victims are abused again."
Supt Moork says that after he was tipped off about the website, he sent e-mails to Microsoft on December 26. But it took a week before the website was shut down.
Backhans says: "They came in during the holidays and there was, therefore, some delay before the complaint reached the right person. We are going to review our routines and staffing during major holidays, too."
Police and Microsoft hope to be able to track down whoever set up the website.