I thought it was just me:
https://www.thestreet.com/story/13908310/1/...&yptr=yahoohttp://www.macrumors.com/2016/11/30/apple-...-calendar-spam/http://arstechnica.com/information-technol...dar-alert-spam/I got one of these in my Calendar application on my MBA last week. I don't use the Calendar so I was surprised to see a notification pop up in the corner on start-up.
[attachment=3347:ad_window.png][attachment=3344:other_UGG_ad.png]
I didn't know where it came from since there was nothing in Mail that corresponded to the ad.
I finally went into the prefs and unchecked the last choice here:
[attachment=3345:Cal_prefs.png]
Also changed to manually refreshing the calendar so these things won't constantly annoy me. Could also turn off Notifications as well, of course that limits the use of Calendar.
[attachment=3346:notif_prefs.png]
(I'm using 10.8.5 on the MBA so your choices may be different in your OS or follow the suggestions in the article.)