Hi Leonie, 

Welcome to Box Community and glad to assist! 

You may see an "Anonymous" user while running a report which shows when anyone who wasn't logged into Box took an action on a Box item. This can occur for various reasons:

• 
  Shared Links: Users do not need to be logged into Box to access a shared link. Thus you may see previews, uploads, and downloads by "Anonymous". This typically relates to shared link activity.


• 
  Email Upload: Users do not need to be logged into Box to upload via email.  As a result, you may see "Anonymous" making many uploads.


• 
  Embed Widget: Users do not need to be logged into Box to preview an embed widget on a website. Thus, you may see "Anonymous" previews.


• 
  API integration: you may see other "Anonymous" actions if you have an API integration that performs actions in your account.

If you are curious for more details around an "Anonymous" action, run a User Activity Report for that action type and select the same date range.

Thanks for posting!