56
Yes, as Ghia says just open a
new browser window and assuming that register.php is in the root directory, enter:
http://www.example.com/register.php
This makes a direct request of the file in a similar way to the robot. Using Firefox you should see the 'direct access prohibited' error that is embedded in the code. With IE you normally just get a 'could not display page' error.
If you check your server log for the exact time, you will see the request for the file has no referrer and has been given a '403' status code (denied).
If you check the log entry for a genuine registration, you'll see the request for register.php has the site as the referer and should have a '200' status code (success).
I'm not saying that this will eliminate robot registrations entirely, but it should stop bots that follow the same pattern as the one in barryc's log.