The data breach was discovered on Thursday morning and led to the system being shut down.
On Saturday, the app was again available to iPhone users, and on Sunday, it became available to Android users as well.
According to Sportadmin's assessment, it is reasonable to assume that personal data has been leaked, even if the extent of the leak is not known.
"In the worst-case scenario, all personal data for all associations and their members are affected," it states on the company's website.
Associations are urged to be extra vigilant about contact attempts from unknown email users or phone numbers.
Sportadmin is used by around 1,700 sports associations in the country and has one million children and adults as members. It is used, among other things, to administer training sessions and association information.
The breach has been reported to the police and also reported to the Data Protection Authority.
