Folksam, which insures every second family home and every second person in Sweden, shared the data with tech giants such as Facebook, Google, Microsoft and LinkedIn.
“We take what has happened seriously. We have immediately stopped sharing this personal information and requested that it be deleted,” Folksam’s head of marketing Jens Wikstrom said in a statement.
The data included social security numbers, widely used in Sweden for everyday activities including banking, and information on who had bought pregnancy insurance, Folksam said.
European regulators have hit firms with increased fines for data breaches in recent years as tougher privacy rules have come into force, such as the General Data Protection Regulation (GDPR).
The breach has been reported to Sweden’s data watchdog, the Folksam said.
It added that there was no indication so far that the leaked information had been used by third parties in an “improper manner”.
Sweden’s data inspectorate did not immediately respond to a request for comment.
“This should not happen and we are now working hard so that it never happens again,” Wikstrom said.