You can change entries because Doodle doesn't authenticate the user – in order to keep the service as simple as possible. When someone enters "Heather" as the user name, Doodle doesn't know whether it's Heather herself at the next visit. Therefore users can change the entries of other users. Doodle relies generally on cooperative behaviour of all users. Normally that's the case in reality. If you want to prevent changes of participants you can choose a "hidden poll". Another way to protect your vote is to participate while being logged into your Doodle account. Also read I want to edit an entry but a small lock appears saying "protected"