I added the following code to my registration.php. Unless I forgot how to count, the number of characters in my domain is also 25. After uploading the changed script, I clicked on our register link and got the following error. So I just put the original register link back. It was worth a try though. The isbot mod is working fairly well. Yesterday, I ended up with over 100 BLOCKED registrations from isbot, with only about 2-3 spam bots that were able to register. So that's not too bad.