After acknowledging the problem Wednesday, Facebook remained silent on the issue for almost 24 hours before issuing an explanation and apology around 1630 GMT Thursday.
A partial Facebook outage affecting users around the world has stretched beyond 14 hours, but was showing some signs of ending early Thursday.
Facebook also said WhatsApp chief Chris Daniels is leaving the company.
From about noon NY time Wednesday, global users encountered only partially loaded pages or no content at all on Facebook's main social network and its related services, including photo-sharing site Instagram and messaging tools Messenger and WhatsApp.
The blackout lasted more than 12 hours for some people, with users in North America and Europe being the most affected.
The outage came amid a period of turmoil for Facebook, which appeared to intensify Thursday with the announcement of the departure of two senior executives at the social network. The outage caused uproar on one of the only working social media sites, Twitter.
In any case, a contact within Telegram confirmed to TechCrunch's colleagues what was already quite obvious: the merit of this sudden growth is the aforementioned problems ("These outages always drive new users"), but is partly attributed to the will of a growing number of users to distance themselves from Facebook. Durov's announcement doesn't mean that three million people have abandoned Facebook, but don't underestimate the network effect if newcomers find they like Telegram and encourage their friends to join. "We are 100 percent back up and running and apologize for any inconvenience", a Facebook spokesperson said. Allegedly, some sort of "server configuration change", according to a company post on competing social network Twitter.
"As we've said before, we are cooperating with investigators and take those probes seriously".
With the New York Times reporting that Facebook is under criminal investigation for actions related to data sharing with third parties, Wednesday was always going to be a bad day for the social network. The company has a large campus of data centers in Prineville.