Just found it today.
I've found that a registered user of the forum is inserted into the main user's table of the blog or site.
My question - is it the right way to handle users as far as security issues or is it a common practice?
In the blog the admin (me) can register users, roles and permissions.
Sorry for the intruding question but I want to learn and understand the system inside/outside.
All is correct. All professional and fully integrated WP plugins use WordPress user system and user tables. This is the most important thing to have a best integrated WP plugin. BuddyPress, bbPress, and all other profile, forum plugins use WordPress users tables. This is the most corect way. There is no any security issue here.
Thank you for the clarification.