the assurance that the largest social networking site was not brought down by unauthorized access by attackers (hacking), three hours after resolving the problem of accessing Facebook for approximately 50 minutes on Tuesday morning.
The company told the Guardian that the problem was due to a systems update for an -unspecified- change, which affected its servers. We moved quickly and now, the operation of both Facebook and Instagram has been fully restored. The malfunction that prevented access to facebook.com, in any way, lasted about 50 minutes and occurred at 8:20 am Greek time.
The service had to deny speculation about an intrusion, after a group whose name has been linked to hacking attacks on well-known websites, Lizard Squad , posted a tweet stating the services that were offline, without however taking responsibility for their status. In addition to Facebook and the photoblogging service, Instagram was not working at the same time. At the same time, other services that accept visitors' entry via Facebook (Facebook login) were also affected.
Source: tech.in.gr

