"Dyn estimated that the attack had involved “100,000 malicious endpoints”, and the company, which is still investigating the attack, said there had been reports of an extraordinary attack strength of 1.2Tbps."
https://www.theguardian.com/technology/2016/oct/26/ddos-atta...
Dyn walked back their claim of 'millions' of sources.
It seems many organizations forget to subtract their baseline traffic from their peak numbers. And some may exaggerate volume for other reasons.
The Dyn attack wasn't that large. Not insubstantial, but not massive, either.