For internet businesses - or any company trading online - it's vital that they can be found easily through web search engines.

The search engine operators want users to get the most accurate results, so websites must often comply with exacting rules.

But Google's changes have puzzled computer users - no-one can work out what they are or why they have been made.

And as the company has at least a 55% market share, that's affecting many people who rely on it to drive business their way.

The problems search engines face is that everyone wants to be at the top of the results list.

Sneaky

That can lead to some websites using sneaky methods to get round the system.

Sex sites often hide text in their pages so their address will show up when the most innocuous term is typed into the search engine.

To get round this, Google uses a sophisticated page ranking system. Instead of just looking for key words, it actually reads the text to determine if the site should be included in the results list.

People have been blatantly abusing the system and working out how to get a good ranking so Google's natural reaction is to change the rules. Andrew Craig, Webuser Magazine

It also works out how popular the site is - how many other sites link to it.

"How it works is a bit of a mystery - it's like knowing what goes into a can of Coca-Cola," says Andrew Craig of Webuser Magazine.

"People are constantly trying to guess what's going on inside Google and trying to manipulate their sites so their ranking is as high as possible."

Every month or so, Google makes changes to try to stop the cheating. This is called the Google Dance.

And occasionally it carries out a fairly major overhaul. The latest happened in November and is known as the Florida Update. It's this which has caused the anger and bewilderment among web users.

Demands

"Google has to, every now and then, change the rules to make it tougher for people to abuse the system," says Andrew.

"Unfortunately some smaller sites have got tarred with the same brush and fallen foul of these new rules."

Sites can put a lot of effort into meeting Google's demands and it can take many months to rise to the top of a relevant ranking.

Now many, including some which have topped the search results for years, find they've dropped out of the rankings altogether.

Maggie Vandenbrekel: Business devastated

Maggie Vandenbrekel is a director of Coconut Connections, which sells coconut oil online.

A search for "coconut oil" on Google UK would bring it up in the top spot.

Now it doesn't even appear in the top 100.

"It's devastated our business," says Maggie.

"People can't find us when they look for us on the search engines.

"If you go to a High Street and you're not sure where a shop is or the shutters are down, you don't buy anything.

"That's what's happened to us and tens of thousands of companies across the world."

University sites

To discover the extent of the problem, search engine specialist Barry Lloyd carried out some tests.

Before the changes, he found that typing "shelving" into Google UK returned a list of shelving suppliers.

Now the top 10 includes shopping directories and various university sites - some looking for shelving for their books!

But typing in "shelving -waffle" gives a much more relevant result.

"Google is very innovative," says Andrew Craig.

"We suspect it's trying to build in a system where you can cut out the general rubbish."

It's nothing new for websites to lose their rankings on search engines, but the scale of these changes seem to have surprised surfers.

Prominently

Some critics say it's Google's way of trying to drive up ad sales - it is possible to pay to make sure your site shows up prominently.

But the company denies this.

Computer experts are already looking for ways to move sites higher up the new rankings.

But until that information is widely available, many online businesses could find themselves being hit very hard.

"We're not going to go out of business because we're a debt-free company," says Maggie Vandenbrekel.