Mac OS X is a secure operating system in that its multi-user and has limits on what some user accounts can do. If an account is setup as a basic user, that user can only hurt himself, not the whole system or other users. However, in the interest of being "friendly" to new users, Apple leaves of a lot of the secure bits off for the first user created and this means that trojans like this weeks can cause some pretty nasty problems on your system.
