user-agent header is added after adding domain in host file

Hi,

request header- 'user-agent: Apache HTTP client (Java version)' gets added to SOAP request automatically when I add the domain to the host file of my machine. I am getting different user-agent values from different machines. 

What is actually happening? 

I checked if it's taking from my machine, but I have installed a different Java version on my machine from what is showing in the user-agent header.