How to prevent spam on forums?

[neku]

I have noticed that most forums get a large number of spam signups, who post junk on the forum. What is most effective method to prevent spammers from registering and posting on a forum, to control spam?

 

[Augusta]

it is to use CAPTCHAs or reCAPTCHAs on registration and submission forms to deter bots.
Anti-spam Plugins can be installed as well.