In the early times, I would dedicate one day a week to cleaning up and deleting the user registration spam accounts. They are easy to spot in a WooCommerce website because the user registration spam accounts are marked as “Subscribers”. Whereas, valid user accounts are marked as “Customers”. Needless to say, I got tired of deleting these user registration spam accounts weekly and decided instead to install a CAPTCHA on the login page.
Using Sweet Captcha, I have noticed a dramatic decrease in user registration spam. But, either solution mentioned should work great for reducing user registration spam, even if you are just using WordPress and not WooCommerce.