Website being spammed

[Nathan Malcolm]

Plugins that also might help against bots are StopForumSpam and Registration Security Question

Ehm, you do know security questions won't work take that from a person who has written game bots to spam bots for fun.

It depends on what the questions and answers are. Mathematical questions (What is 1+1?) are usually a bad idea, but niche specific questions (How many seasons of Dexter were made?) can help prevent spam quite well.

If you know a little PHP you could also modify the script to serve an image instead of the plain text question. I've found that works well for all bots.