Finland's Social Insurance Institution (Kela) has apologised after the use of new type of paper stock could have led to a breach of personal data.
In a press release, Kela said customers details may have been partially visible through the envelope address window in a batch of approximately 80,000 letters sent on 26 and 27 August.
"Although the problem was detected quickly, the letters unfortunately had already been sent to customers. The paper quality has now been changed. We are sorry for our mistake," Kela’s IT Director Jukka Melanen wrote in the press release.
Kela has notified Finland’s Data Protection Commissioner about the error.
About 60,000 letters are printed daily by the benefits agency.