how to disable registration of new users?

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Thanks for discussing this question on a discussion board as i was also looking for the same functionality for my own website. Please revert me if anyone have solution.

We were getting a ton of users created by spammers too. Depending on which version of Askbot software you're running, you can enable the ReCapatcha feature (under Settings > Keys for external services) for both user creation and question submissions. If you enable those two features, it should cut down on the number of spam users and posts.