Go mobile or die seems to be Google's message to websites after a major revamp of its search service to favor mobile-friendly websites.

In a blog post on April 21, Google said changes to its search service will boost the ranking of "mobile-friendly" pages. It also said it will analyze if websites are suited for handheld devices. The changes affect the way websites are ranked in all languages.

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"Today's the day we begin globally rolling out our mobile-friendly update," Google said in this blog post.

"Now searchers can more easily find high-quality and relevant results where text is readable without tapping or zooming, tap targets are spaced appropriately, and the page avoids unplayable content or horizontal scrolling."

Google said the update affects only search rankings on mobile devices and applies to individual pages, rather than entire websites. This means a site might not be mobile-friendly as a whole but still score high in search results because certain of its pages do.

"The intent of the search query is still a very strong signal -- so even if a page with high quality content is not mobile-friendly, it could still rank high if it has great content for the query," Google said.

The new Google algorithm that affects how mobile search results appear will take anywhere from several days to a week to roll out, however.

Google is making this radical change to encourage mobile users to use its apps, thereby boosting its ad sales. Google needs to improve mobile search results to ensure results don't lead to useless sites that frustrate the growing number of people Google searching on smartphones.

Google's search engine defines mobile-friendly websites as those that avoid software like Flash; feature larger text; easy-to-click links; responsive designs; links spaced sufficiently to allow for easy clicking and content that fits the width of a small screen.

Sites that don't meet Google's mobile standard will most likely appear lower in Google search results. Google offered developers a guide to conform to the new criteria.

The change will benefit or hurt millions of websites. Analysts expect this wide-ranging change to be more painful than Google Panda that downranked 12 percent of all sites Google rated low-quality.

Google Panda was a change to Google's search results ranking algorithm first released in February 2011. The change aimed to lower the rank of "low-quality sites" or "thin sites", and return higher-quality sites near the top of the search results.

While analysts said it's impossible to determine how many of the Internet's websites are mobile-friendly, Forrester Research estimates that only 38 percent of all enterprise websites (or websites for businesses with 1,000 or more employees) don't meet Google's criteria. That number doesn't include websites for small businesses that rely on location-based searches.

Google alerted developers to the change in a February blog post. It said the new system "will have a significant impact" on search results.

"While the mobile-friendly change is important, we still use a variety of signals to rank search results," Google said in this blog post.

"The intent of the search query is still a very strong signal -- so even if a page with high quality content is not mobile-friendly, it could still rank high if it has great content for the query."

Several media outlets have said the change will usher in "Mobilegeddon" for sites that don't meet Google's criteria.

There are over 932 billion websites, according to the website, InternetLiveStats at http://www.internetlivestats.com/total-number-of-websites/.

InternetLiveStats noted, however, that 75 percent of all websites aren't active but are parked domains or are in a state similar to this. It defines a website as a unique hostname or a name that can be resolved using a name server into an IP Address. There were 2.92 billion Internet users in 2014.