It’s been an extraordinary day of cancelled flights, disrupted businesses, problems for healthcare and TV stations not being able to get on air (ahem). And all because of an update for Microsoft Windows. So what caused one of the biggest IT failures ever seen – and what do we know about Crowdstrike, the company which released the update?  Ali Fortescue’s in for Niall to discuss it all with our science and technology editor Tom Clarke and data and forensics correspondent Tom Cheshire.     For further background from Sky News, you can read Tom Clarke’s analysis on the questions Microsoft now has to answer here.    Producers: Soila Apparicio, Rosie Gillott Editor: Paul Stanworth