The hacking collective Lizard Squad has claimed responsibility for a devastating attack on Facebook which took the social media site offline… for an hour.
But Facebook says it was to blame.
Facebook, as well as its photo service Instagram and other sites that rely on Facebook login services, went offline around 6am UK time.
They were offline until just after 7am - too early for most users in the UK to notice, and too late for users in America.
For users in Central Europe, however, it was a pretty trying couple of hours.
Lizard Squad, the group which took PSN and Xbox Live down over Christmas and has also carried out a number of other attacks, claimed responsibility.
If only we didn't use twitter to communicate...— Lizard Squad (@LizardMafia) January 27, 2015
But Facebook said that the problem was caused by its own systems:
"Earlier this evening many people had trouble accessing Facebook and Instagram. This was not the result of a third party attack but instead occurred after we introduced a change that affected our configuration systems. We moved quickly to fix the problem, and both services are back to 100% for everyone."
Experts said the initial assumption that LizardSquad were telling the truth is itself illuminating.
"In the same way that it is very difficult for law enforcement agencies to attribute blame for cyber-attacks, it is very easy for hacking groups to plausibly claim any significant online incident as their work," said security expert Professor Alan Woodward of the University of Surrey.
"It is a sign of the nervousness caused by the growing number successful cyber-attacks on major online brands that Facebook quickly issued a denial that the incident was a cyber-attack. It's better to admit a cock up by their own staff than blame it on an outside group."
Earlier, during the outage, Facebook said:
"Facebook and Instagram experienced a major outage tonight from 22:10 until 23:10 PST. Our engineers identified the cause of the outage and recovered the site quickly. You should now see decreasing error rates while our systems stabilize. We don't expect any other break in service. I'll post another update within 30 mins. Thank you for your patience."
"The issue was resolved at 23:10 PST and the site stabilized shortly afterwards. Our internal and external monitoring shows that API requests are being served with normal latency and error rates, in all geographic regions. We are sorry for any inconvenience this may have caused you and the users of your apps."
Facebook is back up now. Life has resumed.