how do I find the source of an unauthorised shared meeting password

I am involved in a strata committee here in Sydney Australia.  We have an issue with unwanted people obtaining the meeting login data and accessing the meeting. We would like to find the source.  

I have been reading up on this matter and realise that we can eject/block  people controlled by the host. Various options available here, including block by email, IP, etc.  Does this work if the Outlook plug in is not installed?

Can you assist in first of these matters?

Thank you in advance.