Note, the contents of users.txt or groups.txt _must_ be wrapped with:
"Out"
{
<file contents>
}

Format of admin account in users.txt--
"<account_name>"
{
	"id" "<name|ip|steamid|clantag>"
	"type" "<name|ip|steamid|clantag>"
	"pass" "<password>"
	"pass_req" "<0|1>"
	"groups"
	{
		"1"	"superadmin"
		"2"	"immunity"
	}
	"allow"
	{
		"1"	"ulx kick"
		"2"	"ulx ban"
	}
	"deny"
	{
		"1"	"ulx cexec"
	}
}

Example of a superadmin without immunity:
"<account_name>"
{
	"id" "STEAM_0:1:123456"
	"type" "steamid"
	"pass" """
	"pass_req" "0"
	"groups"
	{
		"1"	"superadmin"
	}
	"allow"
	{
	}
	"deny"
	{
	}
}



Format of group in groups.txt--
"<group_name>"
{
	"allow"
	{
		"1"	"ulx kick"
		"2"	"ulx ban"
	}
	"deny"
	{
		"1"	"ulx cexec"
	}
}