How Big Can A DDoS Attack Be

On New Year's Eve 2015 the BBC's web domain was subjected to a DDoS attack.  It did cause significant disruption, and it was noticed by many users who took to social media in something of a mild panic. 

The attack interested me not just because the BBC was an unusual target but more particularly for what then followed: those claiming they were the attackers communicated with the BBC technology journalism team.

Part of that communication claims that the attack reached 600 GB/s data rates.