DDOS is form of attack that is unblockable. You can't get prevent it except by improving server capabilities (with large server farms and multiple site IP addresses).
Staying up-to-date on your vBulletin installation is your best way to prevent hacks. vBFirewall is glitchy and out-dated, all it does is add a set of "approved" runnable scripts. You'll notice that some pages in the AdminCP are blocked by vbFirewall now - especially if you check the end of the mod's thread.
You can solve the proxy issue with:
https://vborg.vbsupport.ru/showthread.php?t=201211
https://vborg.vbsupport.ru/showthread.php?t=147280