I host a web application on an Ubuntu 14.04 based VM hosted on Microsoft Azure infrastructure. The webserver is nginx. Recently, someone was trying to probe my server, and later correctly surmised that I was using Microsoft's cloud.
How would they have found this out and how can I mask this information from probers (if at all)?
Note that if I run
curl -I http://localhost, it doesn't give away a lot of information since I've turned
server tokens off.