Philip John

Need to make sure that a site is private for all but the administrators? Just activate this plugin.
There are no settings, no configuration – it just forces anyone that isn’t an admin to go to the login page. They won’t see anything of the site at all. Great for hiding sites really quickly.

Simple Site Lockdown

Provides a really simple mechanism for locking down a site so that it's private to all but logged in admin users.

sander85

This plugin allows to block spammers with the following options:
<ul>
<li>Block spammers by IPs (supports wildcards).</li>
<li>Block IPs that have posted comments marked as spam.</li>
<li>Block comments that contain bad words.</li>
</ul>
Additional options:
<ul>
<li>If comment contains bad words, add the spammers IP into the blacklist.</li>
<li>When deleting spam, add IPs of spam comments into the blacklist.</li>
<li>Similar entries in the blacklist are merged automatically.</li>
</ul>

Block Spammers

Block spammers from submitting comments, by IPs or by bad words.

Simple Site Lockdown vs Block Spammers