To block users from admin side except admin users for specific day,time, and date or permanently.
The plugin Limit Attempts allows you to limit rate of login attempts by the ip, and create whitelist and blacklist.
Spam Master is the Ultimate Spam Protection plugin that blocks new user registrations and post comments with Real Time anti-spam lists.
The most advanced protection against sploggers and spam users registration, is fully WordPress,WordPress MU ,BuddyPress and bbPress 2.0 compatible
Allow members of the forum to selectively have a user's posts and topics hidden from view.