The owner simply stops and then restarts publishing, which generates a new obfuscated/restricted URL, and then chooses a new set of URL recipients.
However, if a restricted URL is distributed further than originally intended, or if an owner wishes to update with whom their calendar is shared, they can reset the URL at any time. Exchange does not control how a URL owner or recipients distribute this restricted URL. When Internet Calendar Sharing is turned on, Exchange can provide a level of security for those wishing to privately share their calendar, by obfuscating the calendar sharing URL, or formatting it such that it cannot be guessed or discovered by searching on the internet.Exchange also bases the Calendar Sharing from a dedicated calendar sub-virtual directory off the OWA vdir, and this calendar vdir is set with HTTP access while OWA is set with HTTPS, so admins do not allow anonymous access to the OWA parent vdir by turning this on. For one, Internet Publishing is OFF by default, and an admin can decide whether the whole org, certain divisions, or even individual users have Internet Calendar Sharing enabled or not, and at what level of detail. Exchange has a number of built-in features to address security concerns an organization might have with anonymous access.In order for Exchange 2010 SP1/Exchange Online (Office 365) to deliver on the promise to let Exchange users share/consume calendars with anybody, even non-Exchange users, we had to relax the requirement for authenticated access and allow for the anonymous access to users' calendar data (within the scope allowed by the Exchange administrator).In Internet Calendar Sharing, can a privately shared calendar really be private? What if somebody forwards the link I sent to another person who shouldn't have access to my calendar? Federated Sharing can also allow org-wide access to free/busy information between orgs based on org-org relationships set up by the admin, as well as the sharing of contact folders. Internet Sharing? Not all organizations wish to enable anonymous (unauthenticated) access to calendar data at any level of granularity, in which case Federated Sharing is the way to go. Within the scope of what the administrator has allowed, a user has the option to publish their data with even less granularity. Administrators can define a Sharing Policy and apply that to the entire org, certain divisions, or even individual users.
Also new is the ability for users to publish their calendar in iCal format to anyone, and for them to subscribe to internet calendars. Exchange 2010 SP1 and Exchange Online (Office 365) incorporate federation to enable secure organization-to-organization free/busy and calendar sharing with other Exchange organizations.