NebuAd was an American online advertising company based in Redwood City, California, with offices in New York and London and was funded by the investment companies Sierra Ventures and Menlo Ventures. It was one of several companies which originally developed behavioral targeting advertising systems, and sought deals with ISPs to enable them to analyse customer's websurfing habits in order to provide them with more relevant, micro-targeted advertising.

At one point, NebuAd had signed up more than 30 customers, mostly Internet access providers, its agreements with providers covered 10 percent of the broadband users in America. Due to fallout following public and Congressional concern, NebuAd's largest ISP customers pulled out. NebuAd closed for business in the UK in August 2008, followed by the US in May 2009. NebuAd UK Ltd was dissolved in February 2010.

Phorm was a similar company operating out of Europe. Adzilla and Project Rialto also appear to be developing similar systems.

NebuAd's platform comprised three main parts: hardware, hosted within an ISP, capable of inserting content into pages, an off-site server complex to analyse and categorise the contents of users' Internet communications, and relationships with advertising networks willing to present NebuAd's targeted advertising.

The system consisted of hardware device installed within an ISP client network. Each device was capable of monitoring up to 50,000 users. Users could "opt-out" of NebuAd's information collection and targeted ads, but there was no way for users to prevent ISPs from sending the data to NebuAd in the first place.

Since ISPs route customers' traffic, it is an important vantage point from which to monitor all traffic to-and-from a consumer using deep packet inspection (DPI). By analysing the traffic, NebuAd reported it gained more information about a customer's particular interests, than less intrusive methods. NebuAd's privacy policy claimed they "specifically not store or use any information relating to confidential medical information, racial or ethnic origins, religious beliefs, or sexuality, which are tied to personally identifiable information ('sensitive personal information')." It also advises, "The information we collect is stored and processed on NebuAd's servers in the United States. As a result, that information may be subject to access requests by governments, courts or law enforcement."

At least 2 customers of a middle America ISP, WOW! noticed unexpected cookies appearing for sites such as nebuad.adjuggler.com, after using Google, which were being read and written, but when WOW's support department was contacted, WOW initially denied responsibility for the activity. After noticing problems with Google loading slowly, and the creation of these non-Google cookies, one customer spent hours trying to disinfect his machine, as he incorrectly thought it had been infected with spyware, but, when this proved ineffective, he resorted to reinstalling his machine's OS from scratch, only to discover the problem did not go away.

On July 9, 2008, WOW suspended the use of NebuAd services to its subscribers.