In my experience, Blacklisting is not the complete answer either. I forgot to mention that some of the IPs used are being spoofed as Bing, Google, PayPal etc. You really do not want the bot to automatically get important IPs blocked out. One time we even had our own server's IP blocked. I since whitelisted those IPs in CSF, however that gives the spoofers a wide open ticket when they use a whitelisted IP.
I did do one thing that helped a good bit. In CSF I blocked CC's. In our case we blocked RU, CN, Ukraine. Again this will not help block them if they are spoofing. And this puts a lot of stress on many servers. The list of CIDR's is quite lengthy. I run dedicated servers so the overhead is not as noticeable as it could be on a shared, cloud or other.
cables24h, you may want to look at the bad_behavior add-on which automatically blocks IPs via htaccess. It works well, but again if they spoof an important IP for your store, it can be detrimental. I use it, although modded for our needs to prevent certain header requests, user agents and to help block the IPs that are initiating script injections.
'better ask why someone choose your website to "spam"'. - If you are lucky enough to have a successful site, with high ranking, you will eventually get sniffed out by the spambots and scriptkitties. They will find you; especially when you advertise on FB, Google and Bing which brings even more notice to our sites. Another reason: Competitors or BlackHat will sometimes do things like this to cause havoc. These signups create spam to a legit email address. Enough spam reports will get you on the RBL; once there, it takes a lot of effort and time to get removed. Until then an ISP like AOL will block your domain from sending anyone with an aol account any emails.
So, Unintended consequences is a real concern for us: if you make it too tight you will either block or alienate your legitimate clients. I try hard to prevent this.
I post his info in an effort to corroborate, not insult. I believe there needs to be many approaches to this issue and there is always going to be a workaround by the other side. A constantly evolving problem.
@Jack_mcsI will post the details of the next signup. I delete them on the fly so I do not have one at the moment. Any hour though, unfortunately. Thanks again for your work on this project. And all of the others too!