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 Recapcha. There are paid modules, but also some free ones, from which we would recommend this one:
First you have to create your own public and private Recaptcha keys on Google Recaptcha:
and then setup them in the module.
If you need help with the implementation, you can order it as a service or contact us to discuss details.