If you run a website or websites, you understand how spam is such a pain in the butt. I guess this is one of the things a webmaster has to deal with. With the technology today, it is a lot easier to create content on the web, including spam. So separate yourself from spam becomes an inevitable task for a web builder.
If you use wordpress, Akismet is THE plugin that you need to activate.
I have forums using both vBulletin and Simple Machine, and Akismet can be used to handle the spam filtering too. For vBulletin, there is readily made plugin that you can download and install from vbulletin.org. And I wrote a simple Akismet API for my Simple Machine board and it worked fantastic.
POW (Plain Old Website)
If you code your (or someone else’s) site all by yourself, there is no readily made “plugins” for you to use. But on the other hand you will have more power to customize since you know the code throughout. There are a few things you can implement to reduce or block spam.
Not trying to discriminate but there are certain countries where a lot of spams are originated from. If your site’s visitors are mainly from US, you can pretty much block all the foreign users from accessing certain pages such as registration, contact, etc.
To identify the user’s country, you can use the IP to country mapping database from maxmind.com and ip2location.com. Both companies provide trial versions of databases and APIs to use. If you like the result, you can purchase a basic version for only $50 from maxmind.
I don’t normally use the IP ban since a spammer usually has multiple IPs to use and it is not that hard to hide the real IP.
Akismet web service
I love Akismet!