Such a mechanism, Leibowitz said, could allow consumers to opt-out of receiving behavioural targeting more easily, rather than having to opt-out on a website-by-website basis.

Leibowitz said a do-not-track mechanism was just “one idea” the FTC “may explore” as part of efforts to make it easier for consumers to manage their privacy online and for companies to be more transparent in how they use personal data.

A one-stop opt-out for online tracking, modelled on the FTC’s own anti-telemarketing do-not-call list, was first pitched several years ago by privacy groups and the idea remains a cornerstone of their demands for more consumer protection online.

The proposals spooked research industry representatives, fearful of its potential impact on the work of research agencies who rely on web tracking technologies to compile data on the size and activity of website audiences, the reach of online advertising and its effectiveness.

In an interview with Research back in 2007, one of the proponents of the do-not-track idea, Mark Cooper of the Consumer Federation of America said the intention was not to frustrate researchers. He said: “We’re interested in people who create behavioural records or profiles to target marketing to the individuals whose records and profiles they have. A research firm that tracks trends is not providing that sort of information to an advertiser or distributor.”

But, as research industry lobbyist CMOR has previously warned, the FTC would need to make it explicit that research is exempt from the definition of ‘behavioural tracking’ as used for the purposes of behavioural targeting.

Leibowitz made his comments at a hearing yesterday of the Senate commerce committee, alongside which senator John Kerry pledged to pursue legislation to give people more control over how their personal information is collected and distributed online.

He said: “Protecting the privacy of consumers online involves much more than the targeted advertising to which they are subjected. Such advertising is just one result of the information that is routinely collected about us online.”

Privacy bills are already being considered by the House of Representatives – the first of which, in its current form, risks making it harder for researchers to reach respondents, thus impacting the accuracy of survey results, according to an analysis by the Marketing Research Association.