Adding images to the question answer challenge is a worth while option. It has stopped my spam registrations 100%. Since the forums require registration, that too has been minimized. Free alternative worth exploring.
I have stopped spam in its place. I can't remember the last time I saw a spam ban come back from the spam service. It's nothing insane but it has provided me months of "real" new customers, 0 bots, and 0 spam. It's a wonderful bliss. I would be willing to package it up as a hook if anyone is interested in it? I haven't done it because I don't know what I should charge. Have a look if you like, URL at the bottom in signature.
I feel everyone's pain about spam. There is nothing like waking up to 40 new members 38 of them spam and 2 posts, one about viagra and the other hot Russian women in my area.
I have a related DNS issue but it's with not receiving email notifications because there's no RDNS (either it does not exist or is incorrect). Spamdyke drops the emails for failing RDNS, I could of course whitelist Invision's domain but since this is such a basic requirement for email this may be affecting others. Addressing the problem locally is better than requesting everyone in the world whitelist *invisionpower.com, I thought I'd try to catch a snippet of the failure when someone replies to this thread so someone can give this to one of the network people.
Sorry for the derail
In addition looking at this from two different points.
# traceroute www.invisionpower.com (from comcast business)
10 66-208-216-86.ubr01b.mchncb01.pa.hfc.comcastbusiness.net (22.214.171.124) 181.249 ms 49.628 ms 54.192 ms
11 lw-dc2-core6-te9-2.rtr.liquidweb.com (126.96.36.199) 58.596 ms 56.627 ms 55.816 ms
12 lw-dc3-dist13.rtr.liquidweb.com (188.8.131.52) 55.563 ms 58.545 ms 61.947 ms
13 infsw01.invisionpower.com (184.108.40.206) 58.997 ms 56.764 ms 55.800 ms
# traceroute www.invisionpower.com (from singlehop)
9 66-208-216-86.ubr01b.mchncb01.pa.hfc.comcastbusiness.net (220.127.116.11) 1.598 ms 1.591 ms 1.576 ms
10 lw-dc2-core6-te9-2.rtr.liquidweb.com (18.104.22.168) 205.685 ms 205.693 ms 205.907 ms
11 lw-dc3-dist14.rtr.liquidweb.com (22.214.171.124) 9.753 ms 9.729 ms 9.716 ms
12 126.96.36.199 (188.8.131.52) 7.192 ms 7.204 ms 7.192 ms