The first method employs an HTTP Cookie and the second method employs IP address filtering at the Paxfire appliance. An ISP is free to make use of these methodologies to ensure that users can opt out, though the cookie method is irrelevant for non-web transactions like email. Security researcher Dan Kaminsky found serious vulnerabilities related to how Paxfire was handling DNS resolution.
The use of HTTP Cookies and IP address filtering at the Paxfire device allows ISPs to provide users with options for opting out. However, this approach may not be relevant for non-web transactions like email. Security researcher Dan Kaminsky identified serious vulnerabilities in how Paxfire handled DNS resolution.