I’ve recommended BestWebSoft Captcha in the past and now regret it after reading this article:
Looks like BestWebSoft sold the plugin and you need to remove this plugin right away and update all your plugins. I do recommend that you have some kind of captcha on your login page for security and use at least the free version of the WordFence plugin. I use Google Captcha (reCAPTCHA) by BestWebSoft
Stay safe, my friends!