It's DNS reflection attack noise: http://dnsamplificationattacks.blogspot.com/2013/09/domain-d6991com.html
This is a good blog for observing the domains and frequent correlation of items in whois and other traits that indicate much of this is done by the same actors.
On 09/23/2013 12:55 PM, Christopher Hunt wrote:
Beginning about 0900UTC we began seeing about 50x our usual DNS traffic. 75% of the traffic is for d6991.com. Does anyone else see this? Who are these folks (WEBNIC.CC)? -chris
