It is treated with a strange method: rename the file...
As a result of improper mounting of the external hard drive, the Ubuntu 16.04 system began to display an error: "E: Distorted entry 1 in list from file /etc/apt/sources.list.d/backports.list (Component)".
It is treated with a strange method: rename the file so that it cannot be read by the system.
The backports.list file is responsible for updates from Debian Backports - the official repository of packages from the testing (mostly) and unstable (in some cases, for example security updates) versions of Debian.
If I understood correctly from WIKI, then it is recommended to be deleted, but I cannot say for sure.
Next, enter the update command: # sudo apt-get upgrade.
Please, if anyone knows the exact solution to this issue, please write down in the comments.