Here are a few of the big brands who were caught napping by the Chrome update that blocks Flash ads

Google's Chrome browser began blocking ads on the web if they used Adobe's Flash animation software from September 1.

Google warned the advertising community on its AdWords blog back in June that the change was happening, and again late last month. Flash is often unpopular because it slows down web pages and browsers.

The company encouraged advertisers to switch their rich media ads over to HTML5 instead, saying this format provides better performance in terms of the impact on browser speed and battery life. Vulnerabilities in Flash software have also seen Flash ads being compromised by hackers, putting consumers at risk.

But despite the warnings, and the tools to help brands and their marketing and ad tech partners automatically convert their Flash ads to HTML5, some advertisers have still been caught out by the update. In the brief time I've been using Chrome since September 1, I've noticed brands including Amex, PayPal, and Pepsi all still continuing to run Flash ads.

I updated my Chrome browser to the latest update today. I was surprised to see that Chrome wasn't blocking Flash ads by default straight away, as all the correspondence had suggested it would happen from September 1.

I had to manually go into my Chrome preferences, then hit "Content Settings," then under "Plugins" I had to make sure I had selected "Detect and run important plugin content." After I had restarted Chrome, the Flash ad blocking began.

(A Google spokeswoman confirmed Flash blocking on Chrome will be a gradual rollout, and the shift to default blocking should happen automatically at some point soon, so I won't need to manually update again.)

I then began browsing some of the world's biggest online news websites, according to Alexa's global traffic rankings. This isn't a comprehensive study, but here are some of my findings in the short time I've been using the setting since September 1.

You notice a Flash ad straight away that has been blocked by Chrome because it'll appear gray and have a big "play" button over the top of it. So few people actually click on ads anyway, and they'll be even less likely to click play to watch the ad move briefly. But advertisers are still delivering those ads.

Here's what should have been an eBay ad on HuffingtonPost.co.uk

When I clicked this ad on ABC News, it was actually a video for Pepsi Max.

An Amex ad on NBC News.

This ad for UK mobile carrier EE was served on the Fox News website.

I was served an ad for P&G's Fixodent (and was a little dismayed at why I was being targeted by a dentures adhesive brand) on CNN.

This Transferwise ad was on Mirror.co.uk.

Business Insider contacted all of the above advertisers for comment. We'll update if we hear back.

Of course, it's not necessarily the brands themselves at fault here. The finger of blame could also be pointed towards the creative agency partners they work with for not moving ads over to HTML5, and their ad tech providers who are still serving their ads in Flash, despite the Chrome update.

More than one in two (51.74%) internet users run Chrome on their desktop computers, according to StatCounter. And more than 90% of rich media ads on desktop use Flash, according to Sizmek.

While the rollout of Flash ad blocking on Chrome is a slower process than some people might have expected, it seems many brands and their marketing partners haven't been quick enough to take notice. If they don't take action soon, they might see a proportion of their digital ad budgets needlessly going to waste.

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