http://dev.maxmind.com/faq/what-are-the-a1-anonymous-proxy-entries/ You'll also want to browse the links up top such as minfraud, chargeback, proxy reporting, vpn, etc. The v2 may help a bit since anyone converting to it may not have actually been blocking on A1/A2 but on !ISOlist or !alpha or !US, etc and/or they wont care to check the traits.