New technology that allows advertisers to track targets

EU clamped down on cookies sparks race to find a replacement, say researchers.

For advertisers it's very important to see which websites you visit: knowing what you read gives them clues on what you may want to buy. Search for "television reviews" on Google and you may find that next time you're reading the news you'll see adverts for the latest widescreen model crop up in the margins. It will be no coincidence.

To do this advertisers used to use cookies - small text files that were saved in a folder on your PC which tracked where you went and what you saw. You could opt out of this system, but unless you proactively turned cookies off in your browser, the tracking would happen by default.