If your business depends on people finding your website, then this will be an anxious development for you.
Google has made changes to the way its search engine ranks sites, and that could send some hurtling down the rankings.
Of course, the company tweaks its algorithm on a daily basis as it battles with Search Engine Optimisation (SEO) specialists who try to game the system on behalf of their clients.
But this is a big change - dubbed "mobilegeddon" by some - designed to favour sites that are optimised for the mobile internet.
Google gave plenty of warning, telling developers about the change in a blog post in February and providing a simple tool to check whether sites were mobile friendly.
The search firm is trying to reassure website owners that this won't be an earthquake which turns their businesses upside down but quite a subtle evolution.
But SEO specialists say this looks like the biggest change since 2011 - and for some that will unearth some unpleasant memories.
For any online retailer, appearing on page one of Google's search results can make all the difference between a profitable business and one heading for the scrapyard.
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