I’ve been suffering from a ridiculous amount of spam comments recently, and so have started using the Akismet spam checker. Already, I am noticing a massive improvement!
Akismet has correctly marked as spam many messages and has successfully ignored those comments which are in fact valid. When comments are marked as spam, you are able to view these and either delete them, or reinstate the comment (at which point, Akismet learns from its mistakes, thus improving the accuracy over time).
I would thoroughly recommend that anyone experiencing spam issues in their WordPress site should check that the Akismet plugin is installed and enable it immediately! 