You can use a Web search service such as Google to search for unique strings of text at your site and uncover other sites with the same content. Alternatively, you can buy a pricey infringement-detection program or hire a public relations firm to do the work for you.

A new free service called Copyscape (http://www.copyscape.com) makes tracking Web plagiarism easier.

Though the practice is fairly widespread, Web plagiarism is clearly wrong. And it's against the law, a violation of both U.S. and international copyright provisions.

Web site owners often devote considerable time and resources to creating their content. Commercial sites leverage it to enhance brand awareness or sell products or services.

One exception to the prohibition against reusing the work of others on the Web is reposting small excerpts of another site when offering comments or criticism. One fallacy is that unless a Web site or page is accompanied by a copyright symbol (a "c" within a circle), it doesn't have copyright protection.

If you're caught plagiarizing the content of another site, you’ll often receive a cease-and-desist letter from a lawyer. But you can also wind up having to pay damages, particularly if it can be shown that your unauthorized use of another site's content caused the owner of the infringed site to lose profits or enabled you to gain profits.

I see Copyscape as a service that helps keep people honest. Launched in July 2004, it's both clever and effective. I found one site that was reusing the content of one of my sites verbatim, without permission, and making it seem that the person had created the content himself.

To use Copyscape, you just type in the address of your page. Copyscape uses Google's technology to search the Web for pages with many words copied from yours. If the plagiarist moved sentences around or changed some key words in a deliberate effort to remain undetected, Copyscape will still find the page.

An offering of Indigo Stream Technologies Ltd., Copyscape exemplifies well the worldwide nature of the World Wide Web. The company is a legal entity of Gibraltar and is a partnership between a Brit living in Israel and an American. I spoke on the phone with the former, Gideon Greenspan.

"Plagiarism is a huge problem on the Internet because it's so easy to do," said Greenspan, who has been developing try-before-you-buy shareware for the Macintosh during the past 10 years.

His company also recently developed the Web content clipping service Google Alert (http://www.googlealert.com), which lets you set up automatic daily Google searches to determine if anyone mentions you, your competitors, your interests, or anything else on the Web that you specify. Results are e-mailed to you.

Copyscape is a free service, as is Google Alert. But just as Google Alert has a beefed-up paid version, Greenspan says that Copyscape will too. With the free version of Copyscape, you have to go to Copyscape's Web site and type in the address of your page. With the upcoming commercial version, you'll be able to set up automatic daily searches and have the results e-mailed to you.

Copyscape isn't perfect. It won't find JPEG and GIF images, QuickTime movies, text contained in Flash animations, or new text on the Web not yet indexed by Google. Still, it's the best low-cost tool out there for controlling how your text-based content is used on the Web.

Other products also attempt to keep people from filching others' words on the Web. Turnitin (http://www.turnitin.com) is targeted toward teachers and other educators, helping them prevent students from getting credit for plagiarized papers. iThenticate (http://www.ithenticate.com) is targeted toward publishers, news agencies, law firms, companies, and nonprofit organizations. Both are available under various pricing schedules.

If you discover another site plagiarizing yours, first collect all evidence to support your case. Next, find the owner of the site. Most sites include contact information. If not, do a Whois search—type "whois" into Google to find Whois directories.

Finally, consider sending a firm but nonbelligerent cease-and-desist e-mail. If that doesn't work, consider having your lawyer send a cease-and-desist letter to the person and the person's Web host. And if that doesn't work, consider having your lawyer file suit.

At the Copyscape Web site, you can find links to additional information about Web plagiarism and what to do about it.