John Wiley & Sons announced Thursday that it had filed 10 lawsuits over the illegal sale of special guidebooks online. Six of the suits involve the sale by students of text guidebooks that are provided only to professors and that contain answers to test questions or assignments outlined in the texts.

The publisher filed the suits after spending several months tracking sales of these materials on eBay, identifying those who were doing the selling, and negotiating settlements with about 150 people, mostly students. Wiley officials said they had no idea how the students obtained the materials, which are not sold at all, but are provided to professors using various texts. No faculty members have been implicated.

Wiley officials declined to release the names of those who were sued. But they said that settlements have been reached with students at Arizona State, Northeastern, Pennsylvania State and Wayne State Universities; the Universities of Florida and Wisconsin at Madison; and several University of California campuses.

"This is a new form of cheating and copyright violation with a Malthusian growth cycle," said Roy S. Kaufman, legal director of Wiley. Students somehow obtain the materials, copy them and then distribute several copies, which are in turn copied and sold, he said.

Even with Wiley's efforts of the past few months, sales of the materials are rampant, he said.

On eBay, you can find these materials by searching for "solutions manual;" there are choices of texts in many fields and from many publishers. Science and engineering fields seem to be particularly hot sellers, with bids for the materials related to many books standing at more than $100.

Kaufman said that most of the people Wiley has approached about such sales have agreed to stop and to pay Wiley to settle its claims. He said that those being sued never responded when Wiley contacted them.