More than 90% of rich media ads (ads that are animated, or change when a user's mouse pointer passes over them) on desktop use Flash, according to Sizmek, meaning if the ad industry hasn't chosen to take action, the majority of ads served to Chrome users won't work properly. 

And with more than one in two (51.74%) internet users running Chrome on their desktop computers, according to StatCounter, the impact of September 1 on the internet ad industry can't be underestimated.

Here's a screenshot of what a website will look like when Flash is blocked on Chrome. You'll notice a "play" button on top of the ads, which appear grayed out. Google says it is pausing ads by default to "improve performance for users" and it's providing advertisers a bunch of tools to help translate their ads from Flash to HTML5.

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Given that the average click-through rate for display ads in the US are just 0.08%, it's clear this is an issue. The creative has been compromised, and users are going to be very unlikely to click to play the ads.

Aside from Google, Firefox has also blocked Flash over security concerns following several instances of vulnerabilities in the software being compromised by hackers. Amazon has also banned Flash ads from appearing on its platform, and Apple has never supported Flash on the iPhone.

The phasing out of Flash could see "shake-ups" in the ad tech space

Eric Franchi, cofounder and chief evangelist at ad tech company Undertone, which specializes in rich media ads, said the fallout from the move away from Flash could see some "shake ups" in the ad tech provider space.

He told Business Insider: "Publishers should begin migrating ad formats and campaigns to HTML5 as soon as possible. Ad tech companies, particularly those in the rich media space, need to do the same. They need to sunset their Flash products and move to HTML5. This is a significant undertaking, so it’s possible we could see some M&A in the space as companies with older Flash-based technology look to upgrade quickly."

"Every single company" in the ad tech industry will be affected by the switch, from supply-side to demand-side, according to Vlad Gurgov, the chief technology officer of Virool, a video ad network.

He says not everybody is ready: "On September 1st, the market will go haywire as supply significantly drops. The most complicated piece here is that there will still be some inventory available to Flash-based content. These are premium placements that are generally full-screen. However, after September 1st the available Flash-based, premium inventory will significantly drop causing the price to dramatically go up. As the tech provider, we will still accept Flash-based creative from our clients however there will be less inventory available that will support it."

US trade body, the Interactive Advertising Bureau (IAB,) has been providing its members with a series of initiatives to help ad tech companies handle the migration from Flash to HTML5. That has included updating its creative display guidelines, revising its HTML5 guide for ad designers and creative technologists, and running events and webinars.

Scott Cunningham, SVP of the IAB and general manager of the IAB's Tech Labs, said publishers have already by and large gone through this shift already some years ago, as they concentrated on converting their sites for mobile. But he says it's the creative shops that will need help.

"Clearly Flash provided different elements. A lot of that can be replicated in HTML5, but it's a different skill," Cunningham said. 

There's another issue as publishers and the ad tech world gets its head around HTML5: File size. HTML5 ads may be more beautiful, and are perceived to be more secure, but the files can be a lot larger than Flash.

Cunningham said: "We recommend publishers do a lot of due diligence around file size. With mobile carrying dating rates, consumers are more in tune with their user experience than ever before ... it's important for publishers to apply strict controls."

The ad industry and online publishers have had ample warning that Adobe Flash is dying a death of 1,000 cuts, but it will now be evident which companies have made the necessary preparations.  

This story first appeared on Business Insider