People who are new to your server would not have an account login name by default. This means they fall into the Guest account and will be assigned the rights as defined in the (Guest) account via the User Editor.
After you have created custom login names for those people you feel deserve their own account, you should consider turning off the following rights for guest accounts to prevent trouble makers from causing problems. Please note that the server will prevent you from assigning certain rights to the guest account as well.
Network:- Add phantoms
- Ignore inactivity timers
- Send complaints
- Duplicate IP's = Do not allow
Transmit:- Broadcast to lobby
- Broadcast User-to-User
- Broadcast Cross Channel
- Send TTS
- Send Wave File Binds
- Send Pages
- Set Phonetic
- Generate Comment Sounds
- Event Sounds Conn/Disc
- Initiate private chat
- Use Equalizer
Channels can also be configured to prevent guest accounts from joining them. Or, you might let them join the channel but you don't want them to be able to transmit into the channel. This is controlled on a per-channel basis via the Channel Admin - Create and Edit menu options.