Changes in network settings were behind the night's crash that knocked out both Facebook, Instagram and Whatsapp for several hours.
The problem did not only affect the services and their users.
Facebook's internal system also crashed and employees' access cards stopped working, which made it difficult to restart the platform.
According to Måns Jonasson, the Swedish Internet Foundation, the crash shows shortcomings in Facebook's security thinking.
- If you can make this type of configuration change that makes it so much, without being able to fix it, then something is systematically wrong, says Måns Jonasson.
Can not be avoided completely
It would take six hours before the error was resolved.
Several IT experts around the world today point out the problem of having internal systems run from the same place.
Måns Jonasson is surprised at how long it took for Facebook to restart the system, even though downtime can never be completely avoided.
- As a society, we invest huge money in our electricity network, but still there are power outages from time to time.
There is force majeure and there is the human factor, what you have to do is minimize these risks and here you have obviously failed because this should not have been possible, he says.
Socially critical infrastructure
Ten years ago, the shutdown at Facebook had not had as great a societal effect at all, says Måns Jonasson.
Today, the interruption becomes more apparent as the platform, together with Whatsapp, has become a socially critical infrastructure for communication.
- It is via Facebook that authorities reach out to most users.
This is where we communicate with each other, where neighborhood groups reach out with information and where bald chains are arranged for missing people, says Måns Jonasson.
- I am convinced that Facebook is ashamed and initiates a fairly large security work to ensure that this does not happen again, he says.
Hear SVT's reporter find out what happened when a "router error" knocked out Facebook - and IT security expert John Bambenek about what he means by "the internet is held together by substandard silver tape and chewing gum" - in the clip above.