If you are looking for a simple and cost-effective solution, we recommend that you use the query with the operator site: or Google Alerts.Keep a record of users who have registered and try to identify typical patterns of spam, such as the time that it takes to fill out a form, the number of requests sent from the same IP address range, user-agents used during registration, user names or other values sent through form selected during registration, etc. Also, it is possible that these patterns are not always concluyentes.Comprueba the log files of the web server in search of sudden traffic spikes, especially if that traffic as you receive a site created recently. Also, try to identify the reasons why more bandwidth and processing power is consumed. Try to monitor your web hosting service free in search of pages infected with malicious software or phishing. For example, you can use the Google safe browsing API to test your service URL on a regular basis. You can also register to receive alerts to your autonomous system. Check the condition of the site. For example, if you use a Polish free web hosting service, would likely are to create thousands of new legitimate sites in Japanese on your day to day service? There are several tools that can help you to detect the language of the sites recently created (for example, language detection libraries or Google translate API version 2). Last (but not least), if you use a free web hosting service, be sure to monitor your services in looking for sudden spikes of activity that might indicate an attack of spam in progress (web design).