The Stop Spammers Plugin checks comments and logins using many methods to stop spammers.
This plugin works incredibly well at reducing spam registrations, but after two months of working great, it suddenly started blocking legitimate users who also happened to be paying customers. I tried several things to prevent this, but ultimately too many customers are getting blocked (and some people are getting blocked from even becoming customers) so I had to uninstall it.
The plugin doesn't provide enough information about why a person was blocked for me to be able to tell the user how to prevent it and the whitelist is pretty useless since a lot of ISPs change IPs regularly so the user would just get blocked again within 24 hours. It would be better if I could whitelist specific accounts so no matter their IP they wouldn't get blocked if I knew they were a good user.
I also think there aren't enough options to customize how it works. For example, almost everyone uses autofill for passwords these days and it was blocking several users. It would be nice to not have a time limit on form submission on just the login form but use it elsewhere when users wouldn't legitimately be ableo to autofill a whole form.
It's also way too easy to lock yourself out of your own site because it doesn't prevent you from doing things that would cause that to happen. For example, I tried to disable the form fill timer by setting it to 0 and instead it started blocking every user that tried to log in.
It's a good idea, but I think the dev should maybe see if someone else wants to collaborate and help clean it up and make it more user friendly and accurate.