The "hosts" file is a local configuration file that assigns the unique name of computers to the IP addresses.
Avira blocks by default the access to this file due to the fact that it is often the target of viruses that modify the host's file to lead users to fake online services.
If you want to edit the file, or if one of your programs needs access to it, proceed as follows:
- Open Avira Antivirus.
- Click the gear icon in the lower-left corner of the window
- Click in the left pane General → Security.
- Disable System protection.
- Confirm the change with Apply → OK.
- Edit the Hosts file as desired.