Fastclick was an advertising network

Advertising network

An online advertising network or ad network is a company that connects advertisers to web sites that want to host advertisements. The key function of an ad network is aggregation of ad space supply from publishers and matching it with advertiser demand...

 which was one of the most visited domains according to Alexa

Alexa Internet

Alexa Internet, Inc. is a California-based subsidiary company of Amazon.com that is known for its toolbar and Web site. Once installed, the toolbar collects data on browsing behavior which is transmitted to the Web site where it is stored and analyzed and is the basis for the company's Web traffic...

 (from the advertisements

Advertising

Advertising is a form of communication used to persuade an audience to take some action with respect to products, ideas, or services. Most commonly, the desired result is to drive consumer behavior with respect to a commercial offering, although political and ideological advertising is also common...

 it serves on other websites). Fastclick paid publishers up to 65% of revenue it generated from ads on their sites. Fastclick's minimum advertising campaign amount was 1,000 USD. It was acquired by ValueClick

ValueClick

ValueClick is a Westlake Village, CA-based online advertising company, which provides online advertising campaigns and programs for advertisers and advertising agency customers in the United States and internationally....

in August, 2005.

Presently, a significant portion of Fastclick's online activity is farming data via a process of depositing spyware on users' systems. It has been known to put ads on sites so one may be ensnared into clicking on it and receiving the spyware.