Fighting Contact Form SPAM
If you use a Contact Form plugin to build and manage forms on your site, you may get a LOT of SPAm thr0ough those forms. To fight this, the best solution is installing an additional plugin to handle detecting and filtering spam form submissions.
There are numerous plugins available:
Add a CAPTCHA block to forms that require users to enter text from an image, or to solve a math problem, before submitting form. (The downside of this is that CAPTCHA can be defeated by more advanced spambots, plus CAPTCHA is annoying to users.)
Analyze form submission data, and if data matches known spam patterns flag submission for review or dispose of submission automatically. (Akismet is a great example of this.)
Check the WordPress Support for more info, as well as links to popular plugins: https://wordpress.org/plugins/tags/anti-spams