Macbook Pro (2010, OSX Sierra) has started prompting me to enter password for DHCP again and again and again All of a sudden my mac has started prompting me to enter my password with the dialog: "Network Configuration needs to update DHCP setting. Type your password to allow this."



I've just recently installed MakeMKV on my laptop... could my Mac have caught something nasty?

As a side note: Is there a way I can find out which process is creating the pop-up window?
You've got a trojan! 
Look at the Directory ~/Library/VideoFrameworks
The Trojan collected your keychain and browser-data there.

The program itself resides in ~/Library/RenderFiles

You can stop it with
launchctl stop fr.handbrake.activity_agent

Did you install handbrake as well or just makemkv?

I would recommend to make a clean install of osx or install your time-machine backup from before the installation of the program.

Update: I cannot comment here, so I try to edit my answer with additional information:

The trojan collects at least the following data:


Keychain files (saved passwords in OSX)
Personal data from every browser on your system including saved passwords
Screenshots


So you really should check which passwords you saved in the keychain and the browser and change them immediately on another computer. You can find the data that it collected in the directory described above in several zip-files.

Do you remember where you downloaded handbrake? Did you use the update function?