Security Code is the secret code which allows you to use AdminBot.
It helps you to protect your group against spammers.
Changing the Security Code
The Security Code can be changed at the Group settings page, read the Security code page for details.
Passing the Code
Pass the security code along with the group name:
llMessageLinked(LINK_SET,SB_SETUP_SETGROUP,"My group name","SECURITY CODE"); // See comments (*) below
(*) It's not a mistake, you can pass the string instead of the key parameter.