According to the local Hudiksvalls Tidning newspaper, girls between 14 and 17 years old are featured in the images, which were likely first sent to the girls' boyfriends and then collected in a single digital folder.
"You feel pressure from guys, maybe you want attention. I did it because the guy just kept nagging," said one of the girls who had nude pictures of herself spread online.
According to the paper, the images were collected in a folder that was subsequently shared among computers at the Bromangymnasiet high school.
Overall, there are more than 100 images featuring at least 30 girls which were subsequently downloaded onto USB memory sticks and can now be found on a number of websites around the world, including pornographic websites.
Calls by The Local to the head of the school for comment were not returned.
The matter has nevertheless been reported to local police as a suspected case of aggravated defamation.
A police spokesperson told the paper that no individual suspects have been identified in the case.
However, even if those responsible for putting the image online are caught, there is little the girls can do to remove the images altogether.
"Everything that ends up on the net can be copied and if someone copies it, it's like having the original," Johnny Lindqvist, an expert on youth and internet, told the Dagens Nyheter (DN) newspaper.
"This is something the girls are going to have to live with and that's something one needs to think about before sharing pictures, both of yourself and of others."
The news comes on the same day that Swedish Prime Minister Fredrik Reinfeldt was due to visit the school where the images were allegedly collected.
However, the visit was cancelled as the prime minister's plane was unable to land due to fog at the Midlanda airport near Sundsvall and instead returned to Stockholm.