A powerful alliance of privacy and consumer groups have likened behavioural advertising² to "being followed by an invisible stalker."

消费群体隐私的强力联盟已经开始着手调查“被无形的追踪者偷窥”的行为广告。

Music lovers might see ads for concerts featuring their favourite artists

They now want Congress to curtail³（缩减，剥夺） the practice of tracking consumers online to tailor（裁缝，使适应） ads more effectively.

Yahoo, Microsoft and Google all use targeted online advertisements.

"It's not just about the right ad at the right time, it's about creating a profile about you," said the Centre for Digital Democracy's Jeffrey Chester.

"These companies want to know about your likes and dislikes, if you are Hispanic, do you vote, are you on a low income or a high income, where do you travel, what do you like to read.

"It's about a system that not only targets and influences the products you buy but is also a powerful and invisible system of digital persuasion⁴ designed to change attitudes and awareness," Mr Chester told BBC News.

The coalition⁵（结合，合并） of ten organisations is expected to call on the government to allow consumers to "opt⁶ in" rather than "opt out" of such advertising models.

It will also seek to ensure no data is collected around financial or health matters. The key, many say, is transparency.

"An individual's data belongs to them and before these companies track you all over the internet, they need to be transparent⁷ about what they are doing and how they intend to use that information," said John Simpson, consumer advocate with the Consumer Watchdog.

Tracking

The call to put limits on such advertising comes as the House Commerce Committee is drafting legislation to improve consumer privacy online.

Congress held hearings on the issue in June. Testimony⁸ was provided by Facebook, Google and Yahoo.

While Yahoo and Microsoft have used behavioural advertising for some time, Google waited until March of this year to employ what is also referred to as "internet-based advertising".

In general the system uses a cookie - a small piece of text that lives inside a web browser⁹ - to track users as they visit different websites.

This information is then used to target online advertising campaigns at consumers because they tend to result in higher online ad return rates.

That means a user who is a keen traveller and visits lots of travel sites would be shown more travel-related ads.

"Golden egg"

A coalition of America's marketing¹⁰ industry trade bodies, representing about 5,000 companies, published a set of seven principles in July to address concerns around the issue.

"The vast majority of what happens online is truly anonymous¹¹ and all marketers and publishers are trying to do is deliver an ad that has some relevancy（切题，中肯） to the person viewing it at a certain time," Mike Zaneis, vice¹² president of public policy for the Interactive¹³ Advertising Bureau told BBC News.

"The beautiful thing is they don't have to click on that advert¹, or pay attention to it or do anything."

While Mr Zaneis agreed more has to be done to educate consumers about the issue, he also warned that pushing for a blanket "opt in" measure would be disastrous¹⁴.

"A broad 'opt in' would be a sea change and it would be a recipe for disaster（促使祸患的因素）. It would kill the goose laying the golden egg.

"The goose is the internet and the golden egg is the free content and services that consumers enjoy and that would be diminished," said Mr Zaneis.

Other organisations included in this broad alliance include the Consumers Union, Electronic Frontier Foundation, Privacy Lives, Privacy Rights Clearinghouse, U.S. Public Interest Research Group, World Privacy Forum¹⁵, Privacy Times and the Consumer Federation¹⁶ of America.