Your iCalendar feed for a list will be accessible by others if you choose to share the list.

If you share a list with a contact, then that contact will be able to access their own feed for that list.

It's worth noting that, even if you don't share your list, some iCalendar-supporting apps could mark your feeds public by default, making the names and snippets of your Remember The Milk tasks searchable. If you want to make sure that your Remember The Milk feeds aren't searchable, we suggest setting your profile and feeds as private.