Techcrunch has an article about the amount of spam has been appearing on the iCloud calendars of unsuspecting users lately.
Apple seems to have no idea that users might not want events from email that resides in the Junk or Spam folders to appear in their calendar. They also seem to believe that a user would never want to delete these events without sending a decline message to the originator.
However, there is an inconvenient but workable solution –
1. Create a new calendar. The name doesn’t matter because it won’t last long.
2. Move the spam events to the new calendar.
3. Delete the newly created calendar. iCal will give you the option to delete without sending the decline notifications.