For much of the Internet era, teenagers who did not want to write their own term papers have turned to the Web to find a ghostwriter.

Now, teachers and principals are using the same tool to catch such cheaters.

In addition to adopting honor codes to guide students' choices, many Washington area schools have installed software that matches the work of students against millions of Web sites, academic journals and even other term papers to ensure that any occurrence of plagiarism will be identified.

In addition to handing in a paper copy of their work to teachers, students log in to the service -- known as Turnitin -- and submit their work in electronic form. Turnitin scans the assignment to ensure that no more than eight consecutive words match any work already in its database. Every paper that is submitted then becomes part of the database to decrease the likelihood that it will be passed on to a friend or sibling.

Several Fairfax County high schools, Washington-Lee High School in Arlington County and George Mason High School in Falls Church have purchased the software. "I think that it deters people," said Orie Bumgarner, 18, a senior at George Mason. "A lot of times, we'll read something and summarize it. Now I have to think about it a lot more and keep it in a way that won't come up plagiarized."

George Mason High purchased Turnitin, owned by Oakland, Calif.-based iParadigms, as part of a schoolwide effort to reduce incidents of cheating, plagiarism and dishonesty. In 2002, the school also adopted an honor code that asked students to add the following phrase to all work submitted: "On my honor, I have neither given nor received any unauthorized aid on this assignment."

Donald L. McCabe, a Rutgers University management professor who has done extensive research on cheating, praised the schools' efforts. McCabe said such strategies help ethics become an everyday part of students' lives instead of something they learn about -- and forget -- on the first day of school.

"It creates a really comfortable environment to know you don't have to worry about other people cheating," said McCabe, founding president of the Center for Academic Integrity at Duke University. "Schools are putting out there values students should strive for . . . to help create this environment of peer pressure and to help them realize the positive environment that can result."

Turnitin's founder, John Barrie, said one-third of all papers run through his site are found to be "less than original," meaning that they duplicate more than eight consecutive words found in some other work. After scanning, the site sends the work to the assigning teacher with the passages in question underlined, so the teacher can determine whether plagiarism has occurred. Sometimes the matches are coincidences that students can explain to their teachers, and sometimes they are the result of failure to properly cite a source that has been quoted, Barrie said. The ease of downloading, copying and pasting from the Internet has made plagiarism more rampant than ever, he said.

"Any institution just relying on an honor code has their head in the sand," Barrie said. "None of our clients are interested in catching students cheating. All of our clients pay us to deter students from cheating."

The software costs about 60 cents a student, so a high school of 1,000 students would pay a $600 annual fee. There are discounts for larger schools and entire districts that purchase the software, Barrie said.

The International Baccalaureate program requires member schools to run student essays through Turnitin, and many area schools have started using the software for other classes, too. That was the case at Washington-Lee, where students have submitted electronic versions of their papers for English, social studies and science classes, said Sandra Munnell, instructional technology coordinator at the school.

Munnell said its use sparked many discussions about when students should cite from other sources, paraphrase or do their own analysis.

"Teachers can model for students when quoted material exceeds their ability to synthesize the information," Munnell said. "It's now a graphical way to show that. You can say, 'Look, where's your understanding of the information?' "

High school students say some teachers ask them to log in and submit every assignment, while others require it only for bigger projects.

For a paper on the Elizabethan era earlier this year, Annandale High School senior Amanda Green said her English teacher told her students to run their rough drafts through Turnitin and fix any passages that were questioned.

Green, 18, who maintains that she does her own work, said she was surprised to learn that some phrases she had written were flagged as having been copied.

"I don't like it," Green said. "I found a few instances where the words might be too similar to something and it comes up as plagiarism." She said she changed the wording to comply with the Web site's findings so she would not get into trouble.

School officials say they hope to impart broader lessons so perhaps one day such policing might not be needed.

George Mason Principal Robert W. Snee said students have raised concerns about cheating for the last couple of years. With the honor code and Turnitin, he said, "we are doing something to change the culture of the school."