In last weeks, there are many shops running on Prestashop receiving spam in Russian language. Prestashop has improved security of contact form in 18.104.22.168 version with this fix, but that helped only temporarily.
Better solution, is to secure the contact with Google reCAPTCHA. If you are using Prestashop 1.7 version, you can use our Google reCAPTCHA Prestashop module that will implement it easily.
After installing the module, you will have to create your own public and private keys in Google reCAPTCHA administration:
and then setup them in the module.
If you need help with the implementation, you can contact us.