A new market for writing has arisen online, and it's targeted at search engines. Content optimized for successful search results ranges from informative articles to incoherent copy stuffed with keywords, a plague that's been labeled search-engine spam.

Popular keywords generate significant traffic for Web sites with related content, giving Web-site owners a financial incentive to host content that ranks near the top of search results. As traffic rises, ad revenue tends to follow, often through ad-delivery services for Web sites like Google's AdSense.

A cottage industry has formed to help people tailor content for search engines. Strike Saturday Inc. advertises software called ArticleBot that, for $30 a month, rewrites copy by substituting synonyms for certain words so that text can be repurposed to score well on search engines. The rephrased text looks different to search engine, contributing to the host site's rank and traffic.

And Hot Nacho Inc. is testing software, called ArticleWriter, that makes sure online content appeals to search engines. "It's basically a text editor that gives an analysis as the article is being written of whether the article looks 'on topic' to a search engine," owner Chad Jones says. The goal, he says, is to help writers create articles that hit all the right keywords, while also being useful and interesting.

Google's Webmaster Guidelines warns against the practice of crafting copy for its search engine: "Make pages for users, not for search engines." But that hasn't stopped many from trying.

Creating content for search engines is one aspect of what's called "search-engine optimization" or SEO, part of a broader business known as "search-engine marketing" or SEM. In sufficient quantity, and absent sufficient quality, SEO content is a form of spam that's aimed at search engines rather than people. And like product-oriented spam, it's controversial.

Blogger Andrew Baio on March 30 questioned on his Waxy.org site the purpose behind thousands of articles that appeared on WordPress.org , a blogging software site. The articles, Baio writes, were "designed specifically to game" Google. Google and Yahoo removed the pages from their respective indexes.

The content in question came from HotNacho.com, and WordPress.org was hosting it in exchange for a fee, according to Jones. He says the content was being used to test Hot Nacho's ArticleWriter software. WordPress founding developer Matthew Mullenweg was traveling and couldn't be reached for comment. At this time of this writing, some 7,000 of the articles could still be found through MSN Search, but the search-result links lead to files that no longer exist on WordPress.org.

Chris Winfield, president and co-founder of SEM company 10e20 LLC, says one of the biggest problems for Google, MSN, and Yahoo is search-engine spam. "That spam consists of pages that are created for the search engines or pages that otherwise trick the end user," he says.

Ani Kortikar, CEO of SEM company Netramind Technologies Pvt. Ltd., says that while search engines may require businesses to employ certain tactics to show up in search results, the tactics should be used to support good content rather than simply to drive traffic.

Netramind charges between $50 and $100 per page of Web content. The company employs some 40 writers in India and four in the United States who oversee quality control. While the company's writing samples won't win any prizes, they're significantly more readable and earnest than the keyword-littered pages that resided on WordPress.org.

But just as legitimate E-mail marketers have felt the backlash against spammers, well-intentioned search-engine marketers--and search engines as well--may suffer if the tricksters continue to thrive. Says Winfield of 10e20, "One of the most important things for any search engine is people having confidence and becoming repeat users."