That may stop other users Also!

Best way according to me is, prevent them at the point if registration. One I was using was Vmail linked below.
https://vborg.vbsupport.ru/showthread.php?t=162642

Best if Someone can update for vb 4.x.

Mind that when you successfully stop them from registering the problem is not over. They then keep banging on your front door as they try to keep in. Causing a lot of server strain and eating costly bandwidth. Add content scrapers and other bad bots to that. I often have around a thousand bad bots online that I would gladly get rid of.

You have a point.

So what to do that? Content scrappers? Link?

You could always log the unsuccessful attempts and then use a mod rewrite script to write the offending ips to a htaccess file on your sites root and this will forbid them

ad 5 questions to the Q/A option this shows one ad 5 and its done

bots cant crack 5 random Q/A

Please look into our free KeyCAPTCHA anti-spam solution:

• doesn't collect data of users like Email, comments, website/blog url, name, etc.
• has never been passed by any bot
  including those that use laundry attacks (redirection/outsourcing captchas, which they could not pass directly, to 3d party human solvers sweatshops)
• in case of cracking, the pool of captchas and its type can be changed by our team without plug-in reinstall on protected websites
• doesn't need typing of squiggly-wiggly texts
• after 1-2 first uses, it is much faster and comfortable for passing than text-typing captchas
• prevents spam instead of sorting out it postfactum
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• one can create captchas from its own images with our on-line designer (fee-based service)
• those, who installed it, switch off other anti-spam measures and moderation
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Built in Q and A is excellent...

If one ever got past Q/A then they must be live...

also use Spam-O-Matic

if they get past QandA and spam-o-matic, then that
is pretty much a live spam issue, not much you can
do about the unknowns except for deal with them
right there on the spot, and move onto the next.

built in Q&A?
i cant find any built in system in vb 4.2.1

In all of our clients' websites, we usually setup some of the methods in this thread. But since a lot of spammers these days are real people, the best defense should include also a usergroup promotion system.

Basically, the default usergroup people get at registration offers limited use of PMs, no links in posts, no images, and so on. You then establish some criteria - number of posts, days registered, etc. - for promotion to the next usergroup. This discourages a lot of spammers, also on very popular forums (we used a setup like this on some of the biggest vB forums).

and in previous days?
the spammers were aliens?
I'm really intrigued by such phrases that are quite frequent to encounter