I'm SVP Product Management at Authentium, Inc. We make the branded security suites that many Internet Service Providers, including Cox Communications, offer to their subscribers. I'd like to take this opportunity to set the story straight on the Craigslist issue that some Cox subscribers have experienced.

In February, we started receiving support calls from users of our branded ESP security suite at ISPs like Cox Communications and Patriot Media. These users had problems accessing the Craigslist.org web site.
Our engineers investigated the issue and found a glitch in our firewall driver that made the Craigslist site very slow to load, or not load at all. (Technical details below)

We contacted Craigslist to learn why only the Craigslist web site was affected and also had our engineers fix the firewall driver. The fixed driver is in QA and will be part of a new release this summer. Our support team has been offering the beta firewall driver to customers who call in and are willing to try it. The support team also assists users uninstalling the software if necessary.

Authentium is dedicated to providing the best possible Internet experience for all users of our security suite, which appears under many brand names. We applaud the efforts of ISPs that go the extra mile to provide free security software to their subscribers and will continue our efforts to make the Internet experience safer and easier.

Technical details:
We found that the Craigslist.org web site sends a TCP packet with a zero-length window. A zero-length window indicates the server is experiencing congestion and cannot handle more data. Our firewall driver responds by sending data only one byte at a time, even after the server increases the TCP window size. This is the glitch we have fixed and are QA testing. Any changes to network drivers must be made carefully, tested thoroughly, and certified before general release.