(CNN) -- Facebook's outage that shut down the site for many users Thursday was its worst since it became a worldwide social-networking powerhouse, according to an engineer for the site.
In a blog post, Robert Johnson said an error in Facebook's automated system for fixing software problems made a problem worse instead of better.
"This is the worst outage we've had in over four years, and we wanted to first of all apologize for it," Johnson wrote.
He said the outage lasted for about 2½ hours for millions of Facebook's half-billion users. It began about 2:30 p.m. ET.
A Facebook spokeswoman said the issue was not related to the one from Wednesday, when problems with a third-party network provider shut the site down, or slowed it badly, for several hours. She didn't elaborate on the nature of Thursday's outage.
On Facebook's blog for developers, a post Thursday had said the site was "experiencing latency issues," or a time delay, with its platform.
In layman's terms, what Johnson described was a situation in which a problem popped up and lots of different parts of Facebook's system tried to fix it at the same time.
That led to hundreds of thousands of requests every second to the databases that handle error reports.
CNN