You can read more about it in Melissa Harrison's article in The Guardian, Why I set about hitting the News of the World where it hurts – its advertising.
Like most good ideas, it's very simple and could be inexpensively copied by campaigning organisations.
It's a web page with tweet me buttons that allows any twitterer to pose a suggested question to the Twitter accounts of the brands who are advertising in (and selling) The News of The World.
Take the country's largest newsagents for example. With a click of a button you can add your voice to the growing number of people who are deeply unimpressed with the paper's actions by asking @WHSmithcouk if they "consider it ethical to stock a newspaper prepared to hack a murdered girl's phone?"
I've just done it and am waiting for an answer. But looking at the number of people who've asked the question before me, I may be waiting some time. Click here to join the list.
Here's a screen grab of the site in case it gets taken down.