Privacy advocates filed a complaint with federal regulators Thursday against tracking and profiling practices used by Google, Yahoo, Microsoft and other Internet companies to auction off ads targeted at individual consumers in the fractions of a second before a Web page loads.

The complaint filed with the Federal Trade Commission by the Center for Digital Democracy and two other public interest groups charges that a “massive and stealth data-collection apparatus threatens user privacy.” It asks regulators to compel companies to obtain express consent from consumers before serving up “behavioral” ads based on their online history.

The complaint, being joined by U.S. PIRG – the national federation of state Public Interest Research Groups – and the World Privacy Forum asks Internet companies to acknowledge that the data they collect about a person’s online movements through software “cookies” embedded in a Web browser allows advertisers to know details about them, even if those cookies don’t have a person’s name attached.

“This idea that a cookie is nonpersonal information no longer really applies in this digital age. You don’t need to know a person’s name to know a person — to understand their likes and their dislikes, the contents of what they read, what they put in their shopping cart. It’s really personal now,” Jeff Chester, executive director of the digital center, said in an interview.

Google launched what it dubbed “interest-based advertising” about a year ago, saying it would make advertising more relevant and interesting by tracking users and categorizing their interests in topics such as sports, gardening, cars and pets. Such real-time ads can be targeted in the 50 milliseconds or less between the time a person clicks on a Web site and the time the page appears.

Advertisers argue that they do value user privacy. A Google spokesman said the company never sells or shares data it collects about its users with any other company. Google also offers a Web page where a user can disable tracking cookies used for “interest-based” ads.

The FTC is already studying the tracking issue, and restrictive legislation may be introduced in Congress this spring.