For as long as there have been internet search engines, there have been people dedicated to manipulating their results. Now, with businesses aware that the difference between appearing in the first or tenth spots on a site such as Google can spell the difference between business success and disaster, the process has exploded into a full-blown industry.

The first "search engine optimisation" techniques, designed to boost the profile of a website by improving its ranking on a list of results, date back to the mid-1990s and the development of the first search engines.

Some of these earliest techniques involved "meta tags" – invisible labels added, usually by hand, to web pages by their creators, ostensibly to act as a guide to a page’s content.

These tags could be picked up by search engines which used them to identify relevant websites. It was just as quickly realised that they could be added to a certain site to distort search results.

However, as the web became larger, meta tags became a less efficient way of identifying useful pages.

Google revolutionised the way search engines seek and sift web pages and their content. The company's "PageRank" system factored in the number of incoming links on a certain page. The more incoming links a page has, the more popular – and relevant – it is likely to be. Moreover, not all links are treated equally – the "value" assigned to each incoming link depends on the number of incoming links on the page it comes from.

That system kept the manipulation of search results in check for a time. But soon a market developed in the buying and selling of links, which enabled website owners to boost the rankings of their sites.

In response, Google and other search engines have turned to other so-called "off-site" measures of a page’s relevancy to determine how prominently it should be displayed in a set of results. Most of these are kept highly secret – in part to deter would be "optimisers".

However, there still exist several methods of boosting a site’s popularity which are widely considered unethical – or "black hat".

"Link spammers" trade in links to sites. Some have created programs that automatically create false posts on message boards which link through to a target page.

"Keyword spam" involves a webmaster cramming a page with "hidden" terms, picked to fool search engines into thinking it is more interesting than it really is. BMW allegedly wrote "gebrauchtwagen" (used car) 42 times on its gateway page for new car sales in a bid to attract surfers interested in used cars. The move led to it being blacklisted by Google.

"Spamdexers" boost pages through the manipulation of the complex algorithms used by search engines to rank sites. These algorithms - the mathematical formulas which dictate where pages appear in a list of search results - rest at the heart of search engines such as Google's.

"Cloakers" seek to fool search engines so that their users are directed to pages they did no expect to see. For example, a company could use this technique to make its own site appear under a competitor's brand name on a page of search results. When unwitting surfers click through, they find themselves diverted to a rival of the company they were originally searching for.

"Google-aters" construct pages solely to appear high up the Google search engine. Often these pages use every trick open to their creators and link through to the actual target site, which will be more conventionally constructed.

"Google bombs" are a type of page manipulated or constructed to appear when certain keywords are typed into the Google search engine. According to Wikipedia, the online encyclopaedia, the first Google bomb to catch the interest of the wider online public probably occurred accidentally in 1999, when users discovered that the query "more evil than Satan" returned the home page of Microsoft, Google’s arch rival. It has never been shown that this was done by Google deliberately.

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