Prevent Spam bots

[bojomojo]

Is there any mod i should install thar helps preventing spam bots or decresing them??

[sylar]

Use the image verification and it will prevent them from registering.

[Dismounted]

Q&A verification is probably more effective than vBulletin's CAPTCHA. Also, you can install "Is Bot" (by calorie), it checks how long the user takes to register.