We use vBulletin 3 for our forums, with a ReCaptcha, a simple "To verify you're a real person, what is the FIRST letter of the English alphabet?" question on signup, and a verified email address required to post. We're also using "TypePad Antispam Beta" to automatically monitor posts for spam content.
Previously this has been enough to keep us down to 1-2 spammers every month or so, but in the last week we've had a sudden explosion of 3-4 every day. :(
Are there any other common plugins or solutions we could try to keep spam under control? I'd rather not turn on moderation for new user's posts, as that'll create a lot of work for us to approve them.
I've checked the spamming users, and unfortunately there's no common factor (IP address, email domain etc) to identify them as spammers like I've seen in the past. They're all from different addresses, they use competent email services like gmail etc, so there's nothing trivial I can do to block them that way.