TraceTogether is explicitly designed to preserve the privacy of every user. In order to achieve this, personal information is only collected once at registration, and is not used except to contact potentially infected patients. Users are only able to request opt-out via an email to a government agency. To trace users the Ministry of Health (MOH) issues time sensitive anonymous temporary IDs that are used to identify the patient to all third parties. When two users of the app pass by, the devices exchange temporary IDs and store them in a contact history log. This log chronicles every user the patient has encountered in the last 21 days, and is stored exclusively on the user's device. Once a user tests positive for infection, the MOH requests the contact log. The user cannot legally refuse to share the log. If a user opts out, their contact information is deleted from the MOH, meaning any log entries they appear in can no longer be matched with them.