The most effective step to strengthen the security of all meetings is to require a password. Passwords protect against unauthorized attendance because only users with access to the password are able to join.
Cisco recommends that administrators maintain their sites with the default configuration that makes using a password mandatory when users are setting up a meeting. This recommendation, with other security best practices, is documented in the guide Cisco WebEx Best Practices for Secure Meetings for Site Administrators and Hosts.
Cisco Webex offers a default, randomly generated password as part of the meeting setup process in sites that do not mandate password protection. Customers are able to override this password with a user-defined password or disable password protection if the site allows it.