comment spam pack is a bundle of four established anti-spam plugins all modified to work with WordPress Multisite.
Keep Your Multisite Network Spam-Free
Help your users fight spam and provide them with peace of mind with these tried and tested plugins:
Simple Trackback Validation provides a simple check designed to combat trackback spam.
The Simple Spam Filter allows you to limit the number of links allowed in comments – a great way to swiftly eliminate the vast majority of comment spam.
AVH First Defense Against Spam blocks spammers before any content is served by identifying them at Project Honey Pot (an open source project to help website admins track, stop and prosecute spam harvesters stealing email addresses from their sites), a local blacklist or the local IP cache. It also checks stopforumspam.com for known spammers trying to post a comment.
Peter’s Custom Anti Spam Image Plugin provides a CAPTCHA solution.
Each of these plugins has been modified to work out-of-the-box with your Multisite installation.