Havas, a major European marketing firm, recently said it would pull its clients' ads from YouTube and the Google Display Network in the United Kingdom after ads began running next to "questionable" content, including videos supporting terrorism.
Marketing giant Havas, whose clients include O2 and Royal Mail, pulled its ads from YouTube last week, while Publicis said it is reviewing its relationship with Google and YouTube and WPP, the world's largest advertising firm, has written to major clients asking them how they would like to respond.
The British government has suspended its advertising on YouTube after some public sector ads appeared next to videos carrying homophobic and anti-semitic messages, prompting a flood of major companies to follow suit.
Google said on Friday it worked hard to remove ads appearing on pages or videos with hate speech, gory or offensive content but with 400 hours of video uploaded to YouTube every minute it did not always get it right.
"Alphabet's Google is facing a serious issue in the United Kingdom with brand safety issues, which has global repercussions", Mr. Wieser wrote in an investor note on Monday.
But he declined to say whether Google would actively look for extremist content, instead of waiting for users to flag it, according to The Guardian.
Havas in the United Kingdom has also pulled advertising on behalf of UK-based clients.
Matt Brittin, Google's head of Europe, the Middle East and Africa, told an industry conference in London on Monday: "I want to take this opportunity to apologise to anyone affected".
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"It is unacceptable that Google is allowing our ads to be placed alongside these videos on YouTube". "Although spending by advertisers who have announced their intention to suspend spending on YouTube and other Google properties is relatively small so far, we think that awareness of the incident will marginally curtail global growth this year versus prior expectations, leading us to reduce our price target on Alphabet slightly, to $950 versus $970 previously".
Google said it would review its controls.
Google's trials and tribulations with its advertisers is just the latest in a long line of tussles the tech giants are having with government and regulators alike globally: from Facebook's accountability for the promotion of fake news, to Twitter's never-ending battle with trolls.
Google did not immediately respond to a request for comment.
Some advertisers create white lists to protect where their ads appear online, one digital ad executive told The Post.
"Google will probably need to articulate goals that sound more like a zero tolerance policy, to alleviate concerns before it can fully recover", Wieser said.
"At the highest levels, we have communicated with Google, Facebook, Snapchat and other partners to encourage their development of solutions".