Hi Mark,
The above issue (see also below) has occurred again with a different file, same plug-in on a different site. However, this time if I use click here to clear all ignored issues and remove, it comes back after rescanning. Note this site running WordPress 3.8.
The two panels below show a before and after view of a file on your system that has been modified. The left panel shows the original file before modification. The right panel shows your version of the file that has been modified. Use this view to determine if a file has been modified by an attacker or if this is a change that you or another trusted person made. If you are happy with the modifications you see here, then you should choose to ignore this file the next time Wordfence scans your system.
Filename: wp-content/plugins/updraftplus/backup.php
File type: Plugin File
Plugin Name: UpdraftPlus - Backup/Restore
Plugin Version: 1.8.5
There are no differences between the original file and the file in the repository.