BRUSSELS: Disquiet among privacy lobbyists over the growing use of behavioural targeting in online ads has triggered a probe by European Union regulators led by German commissioner Gabriele Lowenau.

The EU's advisory body on data protection matters, the Article 29 Working Party , believes targeted web advertising is a "very hot topic" which will come under increased scrutiny next year.

The regulators have already enjoyed some success, forcing Google to cut the amount of time it stores information about past web searches to a maximum of eighteen months.

The EU's move comes as several thousand Facebook members have petitioned the online social network over its Beacon ad system which allows users to see what 'friends' have been buying on partner sites such as eBay and Overstock

The protest has been organised by US civic action group, whose spokesman Adam Green says: "Sites like Facebook are revolutionizing how we communicate with each other in a 21st century democracy.

"But we need to make sure they place the needs and privacy rights of their users ahead of the needs of corporate advertisers."

Despite proclamations by web giants such as Google, YouTube and MySpace that targeted ads are the 'next big thing', media specialists say there are few statistics available on their effectiveness and it is still traffic that counts.

Data sourced from; additional content by WARC staff