IRC has several tools available to keep annoying users at bay. Channels
can be made private or secret (channel modes 'p' and 's'), and can be
made invite-only (mode 'i' - read the online help for /MODE for more
information). Private channels do not have their name displayed on the
channel /LIST, so users need to know the channel name to join. Secret
channels aren't displayed to others in any way - if you're on a secret
channel, the fact of your existence isn't even known outside the channel.
Invite-only channels can only be joined by people who have been asked to
join with the /INVITE command (which is only available to channel operators
on invite-only channels - again, read the help on /MODE for more help with

/MODE * +pi

...would make the current channel private and invite-only, and

/MODE * -p

...would change the current channel from private back to public (visible),
leaving it invite-only.

A channel operator may invoke a "ban" on a user with mode 'b' - this
prevents only that user from joining the channel. On NCF IRC, you can use
the /BAN and /UNBAN aliases:

/BAN aa382 ban userid aa382 from the current channel, and

/UNBAN aa382 remove the ban. Note that bans (as well as /IGNOREs) are placed
by userid, not nickname, since an offending user could otherwise simply
change nickname. Use /WHO or /WHOIS to find the userid corresponding to
a particular nick.

If a user persists in sending unwanted private messages, the /IGNORE
command can prevent you from receiving their comments. The best way to
use this command is again by userid - so, if user aa382 refused to stop
sending unwanted messages, you could squelch her or him with the provided
/SQUELCH alias:

/SQUELCH aa382 completely ignore any sort of message from aa382. You can lift this
restriction with /UNSQUELCH. For finer control of this feature, read
/HELP IGNORE within ircII.

If you are having a consistent severe problem with a particular user,
please report that user to a Freenet Board member (the list of Board members
is available via a menu entry in the "About the Freenet" menu. You can use the
"/WHO", "/WHOIS" or "/WHOWAS" commands to find the userid and real name
associated with a nickname.