AEM 6.5 seems to come with default users
These users have passwords and are not service users.
What is the purpose of the users?
The default 6.0 installation used to come with a user 'formsadmin' that had write permission at /content/dam and was a member of forms-users, workflow-users, and contributor but this user was redundant to the permission set up for the 'dam-users' groups at the same node thus was removed before 6.1.
'fpadmin' had full permission at /content/forms/fp and was a member of 'contributors' but was removed for the same reason.
Could you please confirm, where do you see these users?