MyBB Community Forums

i want to add a plugin which detect spam at registration time

when some one is going to register an question is asked 'what is the name of our country'?

or any other suggested plugins

because at a moment only 5 visitors online

and whos online tab showing 15 guests registering

You may want to search. A simple query of "registration security question" showed a plugin which does exactly this.

You will want multiple questions and you should adjust the questions and possible answers from time to time. Also, there is no concept as "our country" on the internet. Finally, you need to accept all valid responses to your questions (USA, U.S.A., U. S. A., United States, United States of America, etc).

An additional plugin, this one:
http://mods.mybb.com/view/stopforumspam-com-for-mybb

Despite the reviews, it has always worked for me.