I wish it was a simple as just removing them, Unfortunately its is near impossible to restrict the idiots from re-joining under another user name/email address and ip address, back in the early days IP address were assigned to each internet user, Now they change every time you switch you router off and back on, dropping cookies only works if they don't clear them, unfortunately there is no easy fix, But if everyone ignored there attempts to provoke a reaction, then i have a feeling they would soon move on to somewhere else. Just how it is.