The internet advertising technology Phorm has come in for more criticism, following the decision by Amazon to block the system.
Behavioural advertising system Phorm crosses an "inappropriate boundary", according to a public interest research group.
The World Privacy Forum was reacting to news that online retailer Amazon has decided to block Phorm from scanning its web pages. The news is the latest bad news for the technology, which is the subject of a recently-launched European Commission investigation, following claims from UK citizens that it infringes on privacy.
"Phorm is a third party to the transactions on Amazon, and does not have an automatic right to scan for users' details," said a spokeswoman for the forum. "Displaying an ad is one thing, but collecting user information is another altogether. Phorm was crossing an inappropriate boundary."
Phorm analyses internet users' behaviour and posts advertising accordingly. Many in the industry consider it the "holy grail" of advertising, being able to directly market exactly what a consumer may need or want at a particular time.
However, Phorm first came to controversial public light after it emerged BT had conducted tests of the technology on customers - without their permission.
"Internet providers should offer their customers a choice regarding Phorm, and make it clear and up-front," the World Privacy Forum spokeswoman added. "I think most internet users would decline to participate in Phorm if given the choice, which ought to be the case."
