Could you consider adding to the robots.txt
add in a filter to User-agent: *
Disallow /forum/profile.php
to stop bots from indexing the usernames and in lots of cases e-mail address of forum users
(yea I know robots is voluntary, but you got to try)
eg at the moment if you do the following google search, you get a nice list of all publicly listed e-mail addresses (and many duplication)
"site:[
reprap.org] profile.php -hidden"
