I received a message from someone who wanted access to my site and was blocked. I traced his IP to PSI net and removed the block. The person got the latest version of the plugin and thanked me.
20 minutes later, I had a login attempt that was blocked. It was a PSI net IP, not the one that had requested access.
PSI is a commercial internet provider. It provides network access to companies. It is obviously non too careful about allowing servers that run dictionary attacks on websites. PSI is blocked for good, now.