We have added a feature to our Control Pages which will list IPs that we have found to reply to DNS queries. This is to aid customers in securing any open DNS servers that they may have.
We will rescan IPs on a weekly basis, and we will be contacting customers by email when we find vulnerable DNS servers shortly.
There is more information about Open DNS resolvers on our wiki:
http://wiki.aa.org.uk/Category:Open_DNS_Resolvers
Our control pages can be accessed at:
http://aa.net.uk/login-clueless.html
We are happy for customers to run their own recursive or authoritative DNS resolvers, this tool should help where there are DNS servers that are potentially miss-configured and vulnerable to amplification attacks.