The ongoing battle against Spambots

[kurt@triffetdes]

Using 4.2.5
Although the rate of spam registrations has gone down (thanks to the excellent Spambot Stopper), they seem now to be avoiding the moderation step, going straight to active members (but just sitting, no posts). I had 2 dozen emails this morning, but only one in the moderation list on the Vbulletin admin page. I am going to try to create user groups and delete them all at once. One at a time is very cumbersome and there are now hundreds. Using fairly difficult question and answer verification (3 rotating questions), but the bots seems to get by those very easily.
Spam moderation for VBulletin is pretty much now a full-time job. Are there any other plugins that might work?
TIA