Maybe you should try the new reCaptcha that is implemented as part of the core in v1.7. That should decrease the number of SPAM registrations. Note v1.7 is not officially released yet but you can still get the code from here: https://github.com/q2a/question2answer/archive/master.zip
I'm using AntiBot Captcha plugin with the latest q2a version.
it is working very well and has almost stopped spam registrations using bots. (I had 1000 to 2000 bots registrations each day!)
Just install it go to plugin settings increase the "Symbol count" to more than 6 and add some letters to "Character Set". (Characters are case sensitive)
Here is the link: https://github.com/pupi1985/q2a-kk-abc
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