Here are the Vbulletin recommendations:
(Before reading the quotation below, try to enable reCaptcha V2 as @Mirsad said.)
Most people are being hit with a lot of spam these days. Some things
you can do to reduce this are:
Moderate new registrations Admin CP -> Setting -> Options -> User Registration Options -> Moderate New Members -> Yes
Activate email verification Admin CP -> Settings -> Options -> User Registration Options -> Verify Email address in Registration
Upgrade to at least vBulletin version 3.7 or higher. These versions have several Human Verification Options. Admin CP -> Settings -> Human
Verification Manager ->
Image Verification: This is the same Images Verification Captcha as
in older versions of vB, except that this now requires both GD and
Freetype 2 to be installed in PHP.
Question and Answer Verification This allows you to set up a Question
and Answer verification during registration. If done correctly it will
be almost impossible for bots to enter the correct answer.
reCAPTCHA™ Verification This uses the reCaptcha service. You will need
to register with them and get both a Public and Private key.
* Note: As per this announcement, we recommend using the Q&A method with multiple questions. * After you have chosen the method you want
to use and have set this up, then make sure the correct Human
Verification options are set here: Admin CP -> Settings -> Human
And if you have chosen the Image Verification option then you need to
choose either GD or ImageMagick here: Admin CP -> Settings -> Options
-> Image Settings You can go back to the Human Verification Manager to make sure the image is showing correctly.
Note: Both are equivalent. These are also required if you use
thumbnails for attachments or wish to automatically resize pictures
that are too large.
- Ban 'free' email domains many spammers use. Admin CP -> Settings -> Options -> User Banning Options -> Banned Email Addresses
See this thread for a list of commonly banned email addresses:
- Set these options for the Unregistered, Users Awaiting and COPPA usergroups: Admin CP -> Usergroups -> Usergroup Manager -> Edit ->
Can Use Email to Friend -> No Can Email Members -> No
Require Human Verification on Configured Actions -> Yes
Add a new required question to registration. Although there is a Q&A option in the Human Verification Manager, at this time these is no
way to use this in conjunction with Image Verification or reCaptcha.
However there is a workaround for this. You can create a required
profile field to add Q&A to the registration process. To do so, follow
these instructions: Add an extra question to the registration to
prevent bot registrations.
Restrict Email to Friend to Registered Users. Some people have reported that spammers are using the 'Send Email to Friend' function
to spam others from your forums. To reduce this make sure that your
Unregistered, COPPA and User's Awaiting groups have the 'Can Use Email
to Friend' option set to 'No'.
Stop bots spamming through the Contact Us link. Admin CP -> Settings -> Options -> Human Verification Options -> Check 'Contact
Us' and 'Register'
Enabling Spam Management. vBulletin supports managing spam through the Akismet and Typepad Anti-spam services. Both services require an
API key to use. Here is how to obtain those keys.
Akismet - To obtain an Akismet key, you need to sign up for a
Wordpress.com account. This will give you a key to use within
vBulletin. After signing up please see this page for instructions on
retrieving your key: http://faq.wordpress.com/2005/10/19/api-key/
Typepad - Typepad also requires a key to be used. To get one go to
this link here: http://antispam.typepad.com/info/get-api-key.html
Once you have your key, you need to enter it into your vBulletin
Options under: Admin CP -> Settings -> Options -> vBulletin Options ->
Spam Management -> vBulletin Anti-Spam Key Powered by Akismet
Note: Either key goes into the same spot. On the same page set
'Anti-Spam Service' to the appropriate service. You can only use one
service at a time.
Note: Because of recent spam attacks, we strongly recommend that you
combine one of the Image Verification options along with a Q&A as
described in item #6 above.
In addition banning free email accounts (#4) will be a major help as