Since the scale of President Putin’s interference became clear, Mark Zuckerberg has been playing catch-up

The companies that run America’s largest social media platforms have invested billions of dollars to prevent a repeat of the online election meddling that badly damaged their reputations in 2016, as they face new threats from countries such as Iran.

Facebook, Google, Twitter and other big tech companies have revamped their internal systems, hired an army of new staff and opened regular channels to intelligence agencies and to each other’s security teams in the hope of fending off interference in the US presidential election this November.

Although their defences have become more resilient new evidence shows that the internet giants are still stretched to their limits attempting to grapple with much broader and more sophisticated threats than those that they failed to contain