In my Google Calendar, I sometimes find spam events that I never created.
In the screenshot below, you can see that they even managed to put my email address in the "Created by" field.
They are always in the past.
I could not find much information about this problem. This Google support tip tells me to click "Report spam", but there is no such link.
I could simply remove the event, but is there a more long-term solution?
I am using an up-to-date Firefox, on updated Ubuntu Linux, and check Google's "Activity on this account" often, so I think I can rule out the possibility of account hijacking.
The spam events appear in my main calendar (I mean: the first one on the list, the one which does not have an "unsubscribe" link).
The sharing settings for this calendar are as seen below: