Just as anyone who starts for the first time to manage his/her first Blog or even a more greater project (like a Online Community) with Drupal or Wordpress or any other open source application that involves to have administration responsibility , will have to get an eye to users that want to participate and are registering as subscriber or authenticated user that provided a valid e-mail but it seem to you that he is not kosher and you want to see if there is any information you can get out about, searching the web, there are some very easy fre cost online sites.
During my experience as web-admin and site developer even if my specialization do not have security expert qualifications I managed still to provide some suggestions and basic configurations to obtain a suitable degree of security to my clients.
For find out if an email address was abused to spread spam before you may go to Stopforumspam(dot)com and check if the address provided by your subscribe is listed there.
For establishing the origin of the server or client that pinged or scanned your site leaving strange address (url) resolutions with a combination of strange commands appended for attempting to find an open security hole, you may use Ip-adress(dot)com, that in few seconds give you a map and the place ans some more information about who is trying to access your site without evidently open purposes of contribution or participation.
The links and site I have mentioned are free and deliver a volunteer support for all user that cannot effort to pay professional services to control and make your site safe.
One of the indispensable security you should provide with your feedback features of your site is CAPTCHA. It provide you with the free service of analyze the type of comment, the links inserted within and also to check that it’s an human being and not a machine who is providing you with any kind od spam link or content.
