Facebook, Instagram and WhatsApp are back online after spending six hours affected by a global outage.

2GB tech expert and editor of EFTM.com Trevor Long told Deborah Knight the cause of the outage, whether it be an upgrade accident, internal attack or external attack, will likely forever remain a mystery.

However, “we know why it happened.”

“The Internet’s just a series of computers, all of them have a number, and the ‘phonebook’ – the DNS server as we call them – tells your computer [or] phone where to get the information.

“For six hours, the listing of Facebook in that Internet phonebook just disappeared.”

Press PLAY below to hear his explanation in full

Image: Getty