A surprising amount of my work involves helping clients remove spam and preventing future spam. Spam can appear as spam posts, spam private messages or spam registrations. In the case of spam registrations, the spam is usually limited to bogus website URLs for the new “member” that point to spam sites.
Removing spam posts and private message
In general there is no automated way to remove spam posts because it involves human judgment. I can remove these for you with the right privileges by going through your forums, marking these topics and posts and deleting them. Note that if you have a lot of spam that this can get quite expensive. I can estimate the work involved first. Often spam begins to occur after a certain date, which makes it easier to find likely spam.
Removing spam registrations
Large numbers of spam registrations are fairly easily removed directly in the database. The good news here is that there can be removed for a troubleshooting fee, generally an hour of time.
Generally you want to upgrade phpBB as newer versions of phpBB have effective spambot countermeasures. If you need to stay on phpBB 3.0 though I can recommend and install some modifications that will reduce or eliminate these. With phpBB 3.2, the newest version of reCaptcha is supported. This generally works pretty well. My clients often prefer to use additional countermeasures, usually the Cleantalk service. So I can install that extension if you are interested, but it costs $8/year to subscribe to the service.
Most boards to not allow guest to posts. If you do you need an effective spambot countermeasure such as the latest version of reCaptcha. I can help you set this up.
To get started I suggest sending me a service inquiry.