Zoom continues to make rapid changes to their software to improve the security of the program.  A critical change will go in effect on May 30th and requires every Zoom user (Basic and Pro) to upgrade to the latest version of the Zoom client. Go here to download the software https://zoom.us/download. Select the Zoom Client for Meetings download button. If you have not upgraded by the 30th, Zoom will force the upgrade the next time you launch the program or try to join a meeting.

Details about this new version are available here https://zoom.us/docs/en-us/zoom-v5-0.html