How do I keep trolls out of my forum?

[agilent]

I am having trouble with trolls joining. I can remove them after they join, but they just rejoin using a different screen name and email address. I can IP block, but many of them use connections which have changing IP addresses.

Is there any identity software or some type of verification software or hacks, etc.. that might discourage trolls from joining?

I am sure some of you have had problems with trolls so I would like to get feedback on the best way to keep them from joining to start with. I rather catch a troll at the front door than to have to remove them after they have already been posting and creating a disturbance in the forum.

[nexialys]

trolls are human trouble makers... how do you think they can be blocked... the only thing you can do is let them come and go.. they will vanish if they are not blocked or moderated, because their goal is that... bringing attention...

[agilent]

I realize that, but I was hoping someone had some type of method they could share that worked at reducing the number of trolls that join.

For example, an SMS message verification on their cell phone? This way they have to have a cell phone and verify it is theirs before they join. I don't know, just looking for some ideas to discourage them.

I am open to suggestions.

[cheat-master30]

Miserable Users, found here:

https://vborg.vbsupport.ru/showthread.php?t=121886&highlight=miserable+users

It's annoyed and kept away trolls from my forum, because I made it so miserable and forgot to turn it off for them that they took like a month to return...