There are several mods for 6.3/6.4 versions which can significantly help (I use all 4)...
Multiple Identity Detector - As long as they don't clear their old cookies, then you can detect them...
https://www.ubbdev.com/forum/showflat...true#Post107001 X_FORWARDED ver 1.0.1 - Checks to see if they're using a proxy and will display both their real IP and the proxy IP. Only works for transparent proxies though (the majority thankfully), and not anonymous ones.
https://www.ubbdev.com/forum/showflat...true#Post102121 SHOW BANNED - I wrote this one myself. It helps you to keep track of banned users, all the IP's they've used and more.
https://www.ubbdev.com/forum/showflat...true#Post118889 SHOW POST IP - Allows you to search an IP number or range and return all users who have posted under it.
https://www.ubbdev.com/forum/showflat...=true#Post78649 Of course nothing can fully prevent someone who's both knowledgeable and determined to be an pain however, but these mods can go a long way for many problem people.
6.3 would be the one which allows you to install all of 'em (and which is the version I use). If you're using 6.5, then you're on out of luck because I don't think any of them have been updated to it.
