"As far as we can tell 11 customers have been identified and that concerns mobile phone bills for Telia and Halebop customers," Telia spokesman Hans G Larsson told Radio Sweden's P3 station.
He added that the company is not sure whether more people have been affected and that he does not know how the bills ended up on the internet.
"There are probably many factors at play. We have identified which system was affected so we have closed that down and then we have to look at what these 11 customers have in common - why their bills in particular have been viewable. We are working on that," Larsson added.
The problem has to do with the interface between Telia and the customers’ banks, and until the bug is fixed, it will not be possible to review bills on the banks’ websites.