How to Recognize Search Engine Spam
Spam is any attempt to deceive the search engines into ranking a Web page when it does not deserve to be ranked. Types of spam include hidden text and links, doorway pages, deceptive redirection, cloaking, unrelated keywords, keyword stuffing, and link farms.
One of the more obvious ways to spam a Web site is inserting hidden text and links in the content of the Web page (content of a Web site being anything that the user can see). Examples of using hidden text and links are
White text/links on a white background: Putting white text and links on a white background renders it invisible to the user unless the text is highlighted by right-clicking on the mouse. Spammers can then insert keywords or hyperlinks that the spiders read and count as relevant.
Text, links, or content that is hidden by covering with a layer so it is not visible: This is a trick that people use with CSS. They hide spiderable content under the page that can’t be seen with the naked eye or by highlighting the page.
Positioning content off the page's view with CSS: Another programming trick spammers use.
Links that are not clickable by the user: Creating a link that only has a single one by one pixel as its anchor or using the period on a sentence or no anchor at all. There's nothing for a user to click on but the engine can still follow the link.An example of white text on a white background.
Doorway pages: Doorway pages are used to spam the search engine index by cramming it full of relevant keywords and phrases so that it appears high on the results page for a particular keyword, but when the user clicks on it, they are automatically redirected to another site or page within the same site that doesn't rank on its own.
Deceptive redirection: Deceptive redirection is a type of coded command that redirects the user to a different location than what was expected via the link that was clicked upon. Spammers create shadow page/domains that have content that ranks for a particular search query (the words or phrase you type into the search box), yet when you attempt to access the content on the domain you are then redirected to an often shady site that is commonly for porn, gambling, or drugs, that has nothing to do with your original query.
Cloaking: Another nefarious form of spam is a method called cloaking. Cloaking is a technique in which the content presented to the search engine spider is different than that presented to the users' browser, meaning that the spiders see one page, while you see something entirely different.
Spammers can do this by delivering content based on the IP addresses or the User-Agent HTTP header (information describing whether you’re a person or a search engine robot) of the user requesting the page. When a user is identified as a search engine spider, a server-side script delivers a different version of the Web page, one that contains content different than the visible page. The purpose of cloaking is to deceive search engines so they display the page when it would not otherwise be displayed.
Unrelated keywords: Unrelated keywords are a form of spam that involves using a keyword that is not related to the image, video, or other content that it is supposed to be describing in the hopes of driving up traffic.
Examples include putting unrelated keywords into the Alt attribute text of an image, placing them in the metadata of a video, or in the Meta tags of a page, and any time an unrelated keyword is used. Not only is it useless, but it also gets your site pulled if you try it.
Keyword stuffing: Keyword stuffing occurs when people overuse keywords on a page in the hopes of making the page seem more relevant for a term through a higher keyword frequency or density. Keyword stuffing can happen in the metadata, Alt attribute text, and within the content of the page itself.
Basically, going to your Alt attribute text and typing porsche porsche porsche porsche over and over again is not going to increase your ranking, and the page will likely be yanked due to spam.
Link farms: A link farm is any group of Web sites that hyperlink (a link to another part of the Web site) to all the other sites in the group. Most link farms are created through automated programs and services. Search engines have combated link farms by identifying specific attributes that link farms use and filtering them from the index and search results, including removing entire domains to keep them from influencing the results page.
Using invisible or hidden text is a surefire way to get your site banned so it no longer shows up in the engines. The reasoning behind this is that you would want all of your content visible to the user, and any hidden text is being used for nefarious purposes.