Thousands of Google users are exposing the contents of their calendars to the public. The information is indexed by search engines and can include email addresses as well as private events from individuals and businesses. The problem is due to misconfiguring Google Calendar to share its contents with others. However, making the data public means that anyone with your Calendar link can access it. Google shows a warning about this but thousands of users seem to ignore it, allowing their calendars to be available in public searches. Even organizations appear to disregard the notification, ending up disclosing business-related information to the world.
Source: Bleeping Computer