user agent

I would like to ban one spam user from the site. Every time I ban him, he re-register with a new email address. Is there any way to find the user agent of this particular user only so that I can add it in the blocked list.

Improvements to XenForo's user mentions system. This addon is does not handle super-large group membership well. Features: Mentionable user groups. Customizable icon per group (small + large). Membership can be viewed on the front-end. User group may be private, at which point only members...

Currently, the link title grabber is using the user agent of Zend_Http_Client (thanks to my access logs). Could this be changed to something else, to make it look a bit less spammy? While it may not be negative, sometimes it may have slightly negative connotations to a site owner... Liam