So I just received an invitation in my iCloud calendar that was actually an ad for sunglasses. I hope this isn't a thing now.
I have no idea how it happened. They must have somehow gotten my iCloud email address. If it continues to happen I guess I'll have to change it.
Virus? Nonsense. Those are Asian spammers which got their hands on your iCloud adress. As stated, Apple is working on a fix; in the meantime simply deactivate the calendar synch function in iCloud. That's how the spam is creeping on your phone. Do it via preferences or go to http://www.icloud.com and deactivate the calendar function there. The spam will stop after that. Oh, and DON'T simply delete that crap! As soon as you delete it, the spammers get an automatic notification that your email adress is active and they'll send you more, or sell your adress to others.