Apple users have been urged to update their iPhones and other devices, as the effects of a deeply dangerous computer vulnerability still spread across the world. Last week, security researchers found they had found a security flaw so dangerous that fixing it could cause computers to slow down or even need to be re-designed entirely. It exploited a vulnerability in a technology called "speculative execution" – something that can be found in almost every computer made in the last 20 years. As such, computer companies have been looking to fix any vulnerabilities that computers may have, which if exploited would allow attackers to read secret information from a device. Indeed, they had already started before the weakness was leaked, as experts had hoped to do so secretly until the problems had been patched up.