Facebook is being forced to apologise once again – this time for the biggest hack in its history. On Friday it announced that that it had discovered an attack that exposed the personal details of 50 million accounts, including those of co-founder Mark Zuckerberg and chief operating officer Sheryl Sandberg. The attack also gave the hackers access to other services that people logged into using their Facebook account, such as Tinder, Instagram, Spotify and Airbnb. To break in, the attackers exploited an interaction between several different bugs in Facebook's code, tricking the site into handing over the digital keys to individual accounts. When using the "View As" feature, which lets you see what your profile looks like to another user, a video-upload box was incorrectly left activated.