A database of the Koninklijke Nederlandsche Wielren Unie (KNWU) has come into the hands of one or more hackers, the organization reports on its website.
The database contained the data of 90,000 persons, a spokesman explains.
These are members, former members or people who were involved in cycling in another way via the KNWU, such as jury members.
The hacker or hackers have gained access to the database of the old online MijnKNWU environment.
This environment was no longer used since January, but was still kept by the organization.
KNWU members can use the online environment to manage their membership, register for competitions and view results.
Those processes are not compromised because the new MijnKNWU environment has not been affected by the hack.
The stolen database contained names, e-mail addresses, payment details and other personal information, such as residential addresses or dates of birth.
Club membership information was also stored there.
KNWU warns against possible fraud with data
Criminals can use the personal data for fraud, for example by sending fake emails with the request to transfer money.
The stolen information can be used to make such a message more credible, for example with a personal salutation or information about someone's cycling club.
All affected persons were notified by email on Friday.
The KNWU calls on people to change their password in the new MyKNWU environment and to be vigilant against fraud attempts.
People who have doubts about the authenticity of a message or invoice can contact the KNWU to be sure, said the spokesperson.