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Solution:

While the number of attendee's cannot be hidden, the attendee list can be hidden by the host before or after the live session is started.

When scheduling the training session:

1. Click the Edit Options button under the session options section.

2. Uncheck Attendee List in the Attendee Privileges section.
3. Click Save.

Once the training session has started:

1. Click Participant on the top toolbar.
2. Select Assign Privileges.

3. In the View section, uncheck the Attendee list box.

4. Click OK.