The 2.28.3 update performs a logout backup each time time you log out of the application database. You will see a backup called *.nv2_backup_logout. If the name of your NV2 books is named ACME then a backup called ACME.nv2_backup_logout will be created when exiting the books.
You should still perform File > Backup within your application database.
Regards to All,
Martin
