You may have noticed a handful of suspicious push notifications on your iPhone over the weekend -- calendar invites for deals and sales from users with obviously real names like "kcmgweqeq" and "nfbtz."
These invites are exactly what they look like: spam! Your iCloud calendar app is set up to automatically notify you (via in-app notification) of calendar invites, and, unfortunately, the spammers have figured this out.
At the moment, there's no real solution -- you can't mark the invites as spam, nor can you prevent invites from people who are not in your contacts list. You can decline the invites, but any response -- even a negative one -- sends an email back to the spammer and lets them know that your account is active, which means you'll probably end up on a "Definitely Do Send" list somewhere.
There are a couple of workarounds, but they're not perfect. Here are your options.
Prevent push notifications
Your iCloud calendar's default setting is to send event invitations -- aka the spam you're receiving -- to your iPhone as an in-app notification. You can change this setting so that the invitations will be emailed to you instead -- and, hopefully, your email account will be able to filter some of it out. The downside to this method is that you won't receive push notifications for any calendar invites -- even the ones from your friends and family.
To change this setting, go to icloud.com on a laptop or a desktop browser (it won't work on a mobile browser) and log in with your iCloud credentials.
Go to Calendar, click the settings (gear) icon in the lower-left corner of the screen, and choose Preferences.
In the Preferences menu, click the Advanced tab. Next to Invitations, click the radio button next to Email to [your email address]. You will no longer receive push notifications about new iCloud calendar invitations, but you will receive invitations in your inbox.
You can also turn off push notifications for the calendar app on your iPhone. If you use this method, you will not receive invites in your inbox, either.
Open the Settings app and go to Notifications > Calendar. Turn off the toggle next to Allow Notifications if you want to turn off all notifications, or tap Invitations to toggle off alerts and notifications just for incoming calendar invites. (You will still be able to see any invites by opening the calendar app and tapping Inbox in the lower-left corner.)
Make a secret spam calendar and then delete it
If you decline the spam invitations, your response lets the spammer know that you're alive and checking this account -- which means you'll almost certainly get more spam in the near future. There is a way to delete the invitations without notifying the spammer, but it's a hassle. Here's what you need to do:
Open the Calendar app on your iPhone and tap Calendars at the bottom of the screen to see a list of your iCloud calendars.
Tap Edit in the upper-left corner of the screen and then tap Add Calendar. Name the calendar, choose a color if you like, and tap Done.
Go back to the main screen of the calendar app and tap Inbox in the lower-right corner to see the invitations you've received. Tap on a spam invite to open it and tap Calendar to switch the calendar. Move the invite over to the calendar you just created. Do this with all of the other spam invites you've received -- just remember, don't respond to the invite (by tapping Accept, Maybe, or Decline) or you will alert the spammer to your active account.
Once all of the spam invites have been moved to the spam calendar, go back to the calendar editing menu and delete the spam calendar. If you see a pop-up, make sure you press Delete and Don't Notify so the calendar will be deleted without notifying the spammers.
If you don't use iCloud's calendar -- maybe you use a different electronic calendar, or, like me, a high-tech paper planner -- you can simply turn the calendar off.
To do this, open the Settings app on your iPhone and go to iCloud. Toggle off the button next to Calendars. The app will ask you what you want to do with the calendars that are currently synced to your phone; you can keep them on your phone or delete them.
Your calendar will no longer sync with iCloud and you will no longer receive event invitations. You'll still be able to use the calendar app to schedule your own events (from your phone), but you won't be able to use shared calendars.