 This is NewsHour, coming to you live from London. I'm Celia Hatton. Let's return to the massive IT outage that struck worldwide today, affecting companies from the Asia-Pacific, from Japan and Australia, across to North America and Europe. Our international business correspondent, Theo Leggett, is in London's business district, The City. Theo, tell us about the nature of the outage and the effects on the business world.