can't change userid or password for internet connection

[schmitta]

It looks like someone got into my Ubuntu machine and changed my userid and password for my internet connection. When I try to change it back it immediately reverts back to the attacker's UID and PW. I imagine I will have to use an editor to change it where it is located. I need your expertise as to how to do so. Have you seen this type of incident before? Thank you for your help.

[ajgreeny]

I am not sure what you mean by your question; is it your username that has been changed?

You should be able to see the users on the machine by rebooting into Recovery Mode from the grub menu then running command

ls /home

and if you need to reset your user password there are ways to do that including the method shown at https://www.psychocats.net/ubuntu/resetpassword

If you mean that the password used to connect to your router, which I assume is something you did when your ISP contract was set up, I am not sure where you go from here, other than contacting the ISP.