Hi Laurent,
Just had a look. Looks like they are using the ISO 9660 Volume Descriptor #1 field "Application Used" to store the informations :
- URL that tells the latest version
- Delta (the portions of the applications that have changed) between local version and the latest version
- URL of the Delta between local version and latest version
Looks a little complex. May be we can just have a warning that tells us a new versions has been released
?