Mark Zuckerberg’s personal wealth has fallen by nearly $7 billion in a few hours, knocking him down a notch on the list of the world’s richest people after a whistle-blower came forward and outages took Facebook’s flagship products offline. A sell-off sent the social media giant’s stock plummeting by about 5 percent on Monday, adding to a drop of about 15 percent since mid-September. The stock slide on Monday sent Mr Zuckerberg’s worth down to $120.9bn, dropping him below Bill Gates to number 5 on the Bloomberg Billionaires Index. He has lost about $19bn of wealth since September 13, when he was worth nearly $140bn, according to the index. Meanwhile, Facebook has blamed an engineering error for the web apocalypse. Facebook has confirmed that a routing problem throttled its services, bringing operations at its site, as well as that of Facebook-owned Instagram and WhatsApp, to a screeching halt. “Our engineering teams have learned that configuration changes on the backbone routers that coordinate network traffic between our data centers caused issues that interrupted this communication,” the company said in a blog post on Monday. The disruption, Facebook admitted, “had a cascading effect on the way our data centres communicate, bringing our services to a halt.”