Earlier this morning, Google's ad service, Doubleclick, experienced some downtime. During this couple of hours of downtime, Google and publishers across the world would've lost millions upon million of dollars in lost ad revenue.
The simple fact is: Google's ad service is an important, and very integral part of the infrastructure of the Internet itself. Most websites, no matter what content they post, rely on Doubleclick for monetizing their content, so when it goes down, it is felt. The outage affected Doubleclick's publishers for around two hours this morning, before Google jumped on the problem and fixed it up back.
Google says that all forms of sites were affected, from video, display, native and mobile. The outage is rumored to have even affected YouTube ads and Google's Adsense platform, but there were no further details on what exactly caused it.