One of the things you can do that help a bit more against spam, is to only accept submissions that come from your website. This can be done by whitelisting domains on your form.
In FormBackend under the "Settings" tab, you can whitelist domains. Let's say your form is hosted on https://mydomain.com/contact-us - then you enter
https://mydomain.com in the Whitelisted domains field:
If a submission comes in that doesn't match that domain, we'll mark it as spam.
You can see spam entries on the submission page, if you change the filter to "Spam":
The reason for spam is listed in the red box at the top.