Google's DoubleClick suffered an outage today as its servers went down for over an hour.
Several publishers have been affected including The Guardian, Wall Street Journal, Forbes, and The Drum with ads failing to load or the space simply appearing blank.
In a statement given to The Drum Google said: "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 DFP is now back up and running, so our publisher partners can return to funding their content."
It has potentially resulted in massive losses in ad revenue for advertisers.
DoubleClick generated $3.4bn in the last quarter, according to Google's third-quarter earnings report.
Google declined to comment on how it will handle publishers' ad revenue losses.