The network, in a number of residential properties owned by HSB, is run by Telia and has around 11,000 customers.
Telia said that the fault was identified a few days ago while a data switchboard was being repaired.
“It’s serious and completely unacceptable,” said Jan Sjöberg, Telia’s press chief.
It was an external IT consultant, Dan Egerstad, who discovered the problem and reported it to Telia. At first he was told that there must be something wrong with his own computer, but öater on Friday Telia admitted that there was a network fault.
It is still unclear how many people would have been able to pick up other people’s internet traffic. HSB has put a message on its web site, warning customers of the problem.
Jan Sjöberg maintained that it should not be assumed that everyone was affected.
“You need, for example, a so-called sniffer programme and certain knowledge to be able to pick up other people’s traffic,” he said.
Nevertheless, he told TT that Telia’s technicians were “pulling out all the stops” to fix the problem. He did not say when the fault would be fixed.