Yesterday, one of the largest ad serving platforms on the web, Google's DoubleClick for Publishers, went down.
Google said the service was back up and running within two hours:
DoubleClick for Publishers experienced an outage this morning impacting publishers globally, across their video, display, native and mobile formats. Our team has worked quickly to fix the software bug and it's now back up and running, so our publisher partners can return to funding their content.
But the news and the result of the outage cost publishers dearly. Business Insider said it cost $1 billion per hour for publishers globally. adAge said while it cost some big time, there were those who benefited from it that were not using DoubleClick.
Many sites, including this one, use DoubleClick to serve ads.
Forum discussion at WebmasterWorld.