本文研究盜印電腦軟體行為之市場後果。模型中之軟體生產商面對一些“盜印集體”。這種盜印行為改變市場的需求曲線，但不單純地使曲線左移。本文處理此問題的方法，能兼顧到盜印行為之“深”與“廣”度。結論之一是盜印行為使售價上升；但若盜印行為已很嚴重時，減少盜印反會使利潤下降。這些結果能解釋近年來美國個人電腦軟體市場裡的一些有趣現象。

　　　　　This paper studies the market effects of unauthorized copying of commercial software. A model is constructed in which a firm facesconsumers some of which form "copying groups". Such copyingmodifies the demand for originals but does not simply shift it to the left. This approach takes into consideration both the extensive and intensive dimensions of copying. A finding of the paper is that pricetends to increase with more unauthorized copying; moreover, making copying more costly to potential violators in the face of alreadyrampant copying may actually lead to less profit. These results canexplain certain recent, interesting phenomena in the U.S. PC software industry.