People can find out a lot on the internet. More and more, the internet is finding out a lot about them. Google said this week it will follow Yahoo and AOL and tailor web adverts to its users’ preferences, divined by monitoring their individual browsing patterns. This causes excitement among advertisers – and sends shivers down the backs of privacy activists. Both are justified.

Much advertising is utter waste. Any advert that does not help people find things they want to buy amounts to money spent in vain by the advertiser and time lost (and sometimes mood soured) for the consumer. “Behaviourally targeted” advertising can therefore in theory be a great improvement: the advertiser gets more value for money, consumers avoid ads for things they have no interest in, and businesses that depend on advertising revenue, such as Google but also the media, gain a more solid economic footing.