Arggghhhh, now some waste of skin has figured out how to spam people by sending iCloud calendar invites to random email addresses. I just got an ad for Ray-ban sunglasses in my calendar. I like to refer to Spam that's sent by real people to the wrong address as "Spork." I'm not sure what to call this new type. Maybe "Spam Lite" or "Spam Singles"--both of which are real things BTW. Ya, Spam Singles sounds good, but moving on...
Thanks to user duozmo on stackexchange.com for the solution. To prevent this type of spam:
Log into iCloud on the web, open your calendar and go to ⚙ > Preferences. Under Advanced, you’ll find an option to receive calendar invitations by email instead of straight into your calendar.
This should allow you to delete calendar spam like regular email spam.
The other annoyance is that you can't delete or modify these since only the organizer can do that. To remove any spam you get this way.
1. Open the Calendar app from your Mac (not the iCloud web interface)
2. Create a new calendar (e.g., called "Junk")
3. Right-click the spam event and choose the Calendar option. Select "Junk" from the list of calendars and the malicious event will be moved.
4. Delete the Junk calendar entirely (without notifying).
