Thank you ! from what I read though it won't stop malicious bots as they will ignore the robots.txt file.
 
A lot of sites have a script to make you identify a series of  alpha-numerics in pictoral form (usually 3 or 5) to access the site, or download stuff. Passwords (like Renderosity's) are another way to go but then there has to be a record and a registration process somewhere. I don't  have any plans to write a script like that or actively look one up but if happen to run across one I 'll be sure to let you know.  

even then a reference to a specific page in say google might sneak around the logon...