Chapter 1 What’s New for FortiOS 5.2.1 : Authentication : Limiting Guest User Accounts
  
Limiting Guest User Accounts
A new option to has been added to the guest user group where the administrator can restrict the maximum number of guest accounts that can be created. After the limit is reached, the portal administrator will need to remove some expired accounts. The number of accounts can be set from 1-1024 or left as unlimited (0 in the CLI), which is the default setting.
 
In the web-based manager, the lower limit is restricted if there are existing group members. In order to set a lower number, guest accounts must be removed prior to the limit being set.
Syntax
config user group
edit guest-group
set group-type guest
set max-accounts [0-1024]
end
end