The website DownDetector.com said Facebook began having issues at about noon Eastern time.
That said, the only Facebook-owned app that is now not experiencing any problems is WhatsApp.
DSoS is short for distributed denial of service, a cyber attack by which multiple computers flood a website's servers in an attempt to take it offline.
Facebook acknowledged the issue in a tweet.
It's worldwide, but appears to be hitting the USA and Europe particularly hard.
Facebook has been suffering from outages across the world since around 12pm ET Wednesday.
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Facebook users logging on to social media site reported getting a message stating that the site was doing "required maintenance".
One said: "Facebook, Messenger and Instagram are down and here I am ranting on Twitter".
Instagram is also owned by Facebook Inc.
More than a third of Facebook users affected by the outage reported that they were experiencing a 'total blackout'.
This is a developing story and will be updated as more information becomes available. Others report zero problems while someone directly connected to them has an issue.
It is still unclear when two of the biggest social media networks will be back up and running.