You ban them all because... proxies or what? I really hate getting hacked... most of the time when it happens to my site they somehow manage to get a hold of the cPanel password. And believe you me, it's not a weak password... alphanumeric, both cases, the works. Our host sucks... but we have to live with it, any ideas on this end of how someone could be getting the password?
Many ways, keyloggers brute forcing or just coming it without the password at all. Cpanel is known to be the source of many cracks just because it's so widly used and allows you so much access to the system.
Most of the guys that are serouis about their servers don't even run a control panel script .