I'm also using the forum for some years. I would strongly suggest you to update to the current version (1.7.3) since some security problems (ie, JavaScript-Injection) were resolved. Also the optional captcha is a quite nice thing.
Go to the admin-area > forum settings > advanced settings
In the last line you see your current version.

Thanks, Alfie. Trust me, I have considered updating to 1.7. But I decided to wait for the 2.0 release, since it will be a much greater upgrade. Also, I have a few extra fixes and have made some adaptations to the forum to fit my needs, which means there is extra work doing an upgrade.

As for Captcha, I already have the "addition" protection for non-logged in users implemented.

Per