Normally the who command will show differences between opers, channel ops and users. When this is enabled it applies new rules to the server.
1) '*' not shown for IRCops when command is issued by someone who is not an IRCop or channel op.
2) Even if you are in the channel, and even if the channel isn't secret/private the command works as if you weren't in it and it was private if you are neither a channel op nor an IRCop.
3) 'WHO #<channel> o' is disallowed unless you are a channel op or IRCop.
/as security set whochan off
This tightens down the security for those implementations that are more vulnerable to external scripting and use of mass advertising.