When creating your Vevox meeting the default identification setting is Profiles Off.
You can change this option in the settings menu
Profiles On requires all participants to set a first and last name when entering the session. When a participant sends in a message their name will be tagged to it so all other participants can see who has sent the message. The downloadable report will also show this information as well as identifying the names of participants along with how they voted in polls.
Profiles Off is completely anonymous. When participants send messages there will be no indication in the app or in the reports about who sent the messages and likewise for polling, the reports will not display any information on the identity of the participant.
You can change the profile settings between On and Off at anytime however doing so will clear your current results. If you already have results in your session you should download the report before changing the profile setting to avoid losing any data.