Difference between "distinct computers", "any computer" and "single computer"

I am trying to set up notifications to detect a possible virus outbreak around the corner.

When I am setting up the notificatioin for "Risk Outbreak", I see there are three options for Outbreak Type:

1. Occurrences on distinct computers

2. Occurrences on any computer

3. Occurrences on single computers

Can you tell me what is the difference between "distince computers", "any computer", and "single computers". This is really vague. Please give an example.