We do something a bit different with threads, JustDave gives unregistered lurkers/spammers/spiders fake email addresses.
This:
- keeps your members email addresses private to ony those regged members and
- fills the spammers email lists with bad email addresses, effectively ruining them for their business purposes.
Visit
www.ubbdev.com while not logged in, click on a profile and you'll see what I mean. bah, he changed it to where you have to be logged in to view a profile, which is just as good, but without the spam killer effect

robots.txt is only useful for the legitimate spiders, spammers ignore them. .htaccess is not reasonable for most sites. and the spider/robot lists aren't for the spammers who change their tactics daily to combat anti-spoam measures.