3 ms·

Any recommendations?

• ve55 8y ago
  For most situations at most scales, there's a lot of simple open source captchas that should work just fine. If you're working on something that has high potential for dedicated abuse, there are some paid ones that will work well too. I can edit this post with links in a moment. But a captcha is just one line of defense, and you can take a lot of other things into account, like threat score of visitor IPs, verification methods like email, phone, etc.
• altfredd 8y ago
  If you want to simply limit amount of unwanted traffic, implement conventional image captcha with some minor twist. State-of-art bots do not (yet) have a human-like AI, so you will be safe(r) until someone adapts all existing bots to solve your modification. If you want to hinder determined (but inept) adversary, impose reverse time limit: make your captcha a bit complex and deny answers, that arrive too fast. Legit users will spend a bit of time to solve captcha. Machine-learning-driven bots will blaze it. In addition to measuring speed of filling captchas you can measure amount of user time spent on other actions on your site — in process making your bot detector increasingly similar to Google's reCAPTCHA. In general look for behaviors, distinguishing legitimate users from malicious. Hint: having Google account might or might not indicate a legitimate user, but it is probably more efficient to ask users for it directly than in roundabout way by using reCAPTCHA.