Just a little side note, using /mode +b for a ban will prevent the nick/address from joining, but if they are already on the channel when the mode is set, it will not kick them.
If you want to kick them off as well, you'd have to use /kick <channel> <nick>, along with the /mode +b command
An alternative to this, is to use /ban -k <channel> <nick> <mask>
As mentioned before, the <mask> parameter is optional
The -k switch kicks the nick before setting the ban
/help /ban for more information