Google has the power to make or break businesses. Even the slightest tweak to its complex algorithm can catapult a company to instant Internet stardom, or forever banish it to the bottomless pit of irrelevance.

As the online giant gets ready to roll out the latest modification to its secret search formula, "mobile-unfriendly" businesses should be shaking in their boots - or work through the weekend to get with Google's program.

As of Tuesday, the world's leading search engine will begin ranking sites according to their "mobile-friendliness."

Friend or foe

But what's considered mobile-friendly - or unfriendly, for that matter? If you have to squint to read this on your smartphone, or are having trouble clicking links, because everything's so small, then, you guessed it, the site and your phone most likely don't qualify as buddies.

To secure a place in Google's inner circle, websites must load quickly on mobile devices, and users must be able to navigate content without spraining a thumb. Sites that don't fit this bill will be relegated to the last pages of its search results.

Although the new formula will only affect mobile device searches, the move could completely change how, where and on what people spend their money. More and more consumers are turning to their phones when deciding where to eat, shop and travel.

According to research firm comScore Inc., 29 percent - or nearly 19 billion - of all US search requests made in the final three months of last year were done on mobile devices. Google was the go-to search engine for almost two-thirds of users.

Mobile or die

But even though smartphones have been around for nearly a decade - eons in Internet time - many companies are still stuck in the proverbial online Stone Age.

A study released by the Internet Advertising Bureau UK (IAB) last month, revealed that one out of ten of the top 250 UK brands fall into the "unfriendly" category. That's almost like displaying a "Sorry, we're closed"-sign, when the store is actually open. All the more worrying, then, that more than a third of the UK retailers surveyed didn't have mobile sites that allow transactions.

Experts warn that Google's new algorithm could unleash a "Mobile-geddon."

"Some sites are going to be in for a big surprise when they find a drastic change in the amount of people visiting them from mobile devices," said Itai Sadan, CEO of website-building service Duda.

Editor-in-chief for trade publication Search Engine Land, Matt McGee, called the tweak the most significant change that Google has ever made to its mobile search rankings.

It's all about being seen

Past cases show that even powerful companies are defenceless against the will of the Internet mastodon from Mountain View, California.

eBay felt the pain last May, when Google rolled out an update to its spam filter. Going by the deceitfully cuddly name of "Panda 4.0," the release squashed the online auction giant's search result rankings, or "visibility," almost overnight.

According to search analysis company Searchmetrics, eBay was 33 percent less likely to be noticed by potential customer, landing an uppercut to its sales. The tweak, Baird Equity analyst Colin Sebastian estimated, shrank the ecommerce company's gross merchandise volume by around 5 percentage points, Business Insider noted earlier this week.

An even more crushing example was concert ticket sales platform Songkick, which saw its visibility drop by a devastating 75 percent. At the other extreme, entertainment news site Zimbio's rankings shot up an eye-popping 500 percent.

Every time Google tweaks its buttons, it triggers an uproar. To keep complaints to a minimum, this time it has created a step-by-step guide and a tool to test if sites are truly mobile-friendly.

Business owners will have little choice but to adapt, or face the threat of extinction.

"Availability is part of relevancy," Gartner analyst Whit Andrews said.

"A lot of people aren't going to think something is relevant if they can't get it to appear on their iPhone."