I seldom hear from vendors that are targets of negative comments in this column. Every now and then I get a flame, and once in a blue moon someone actually wants to talk seriously about the issues I raised. NebuAd, the advertising start-up I criticized recently, turns out to be one of those blue moon companies.

A few days after the column (“An invisible abomination,”) appeared in early July, I got e-mail from one Ben Billingsley, who identified himself as involved in marketing for NebuAd. Billingsley said he had read the column "with interest" and wanted to know if I would be open to talking with NebuAd's CEO. No flame-age, just a polite offer, so I accepted. Billingsley set up a conference call in which I was able to have an informative conversation with him, Chairman and CEO Robert Dykes and President of Advertising Systems Kira Makagon.

I wrote the original column using information on NebuAd's Web site and from a number of online comments and blogs. Dykes did not say I had gotten things wrong — he just offered to describe what the company did. Based on the description, I'm not sure I did get the basics wrong. But what NebuAd is doing is not as bad as I feared, though not as good as I would like either.

Basically the company is monitoring all sites you visit and builds up a profile of your interests. Based on what Dykes said, the profile is quite coarse and basically keeps track of the categories of the sites you visit. They categorize the sites based on their review and based on scanning site metadata and text. NebuAd carefully does not include any categories related to health issues, politics or adult topics, Dykes says. Thus it winds up with a profile tied to an IP address (which they hash before storing) with counters indicating how often particular types of sites are visited. This lets NebuAd serve up an ad for a car even if you are visiting a Web site focused on quilting if your previous Web activities included visiting a lot of car-related sites.

The company also keeps track of session-based activities — for example, how many people visited Ford, what they saw and what else they visited. NebuAd provides this info to ad agencies but only after double hashing the IP address to make it essentially impossible for the agency to link the activity back to an individual IP address.