All forms created with the Form Builder automatically support Honeypot Form Protection. Honeypot is generally an effective first line of defense against spam/DDOS attacks.
Honeypot will add fields to your form that are invisible to the user. However bots will input values in these extra fields. When the form is submitted, verify that the honeypot fields are empty. If they have values in them, they were submitted by a bot/spam/attacker and can be discarded.
Another feature of KaratEmail's spam protection is that the system limits multiple submissions sent within a short time-span. If someone tries to send 1000 submissions in 2 seconds, the will be blocked!