Benjamin Mayo, writing for 9to5 Mac:
Apple is rolling out a fix for the iCloud Calendar spam issue that has plagued users over the past few weeks. On iCloud.com, the company has added a new Report Junk feature. This lets users remove spammy invites from their calendar and reports the sender to Apple for further investigation.
The feature is currently only available on Apple’s iCloud.com Calendar web app but it is likely to roll out to the iOS and Mac native Calendar in a future software update …
Although the change will no doubt come to iPhone and iPad natively soon, for the time being users must visit iCloud.com in their browser to access the feature. The Report Junk button appears for calendars invites from unknown senders; that is, invites from people not in your contacts.
Upon selecting to report, a confirmation alert appears to explain what has happened. The alert says that ‘Junk invitations are automatically deleted from your Calendar’.
I haven't received any calendar spam in several days, but this is a nice tool.