Account access problem

[Spectrum]

I've got a single admin account, and have just created a new user account.

For some reason, the new account (even a temporary guest account) is able to access ALL of my files in the Admin account! The only folder where access is blocked is my DropBox folder.

Interestingly, as expected, the admin account cannot access the new user account folders (except Public and Sites).

Why? And how do I fix it?

This is on OS 10.5 (Leopard).