Adata transgress on the Civil service Pension scheme portal last week meant some members of the scheme received personal data relating to other members.
Capita said 138 members of the scheme either received personal Annual benefit Statements data belonging to other members and/or had their personal data seen by other members.
In an update to members, the firm said the breach was identified quickly, ABS functionality was immediately suspended, and a full investigation undertaken.
The firm said all impacted members would be written to by 9am on 3 April 2026 via secure message. It said that, for members who haven't received correspondence, this way their data was not impacted in any way.