軟體侵權的現象在現今軟體產業中已是個非常嚴重的問題，嚴重影響到軟體開發業者與資訊科技智慧財產權的發展，許多公司因此損失了相當多的潛在利潤。儘管如此，軟體侵權的擴散可能會影響到合法軟體的擴散，亦即軟體侵權者可能會影響潛在使用者採用該軟體，並且這些採用者中有些可能會成為購買者。本研究之擴散模式是用來描繪合法與非法軟體的擴散軌跡，此方法能夠估計侵權者的數量，與受侵權者影響而採用合法產品的比例。本文運用此模式研究英國軟體的擴散型式，其結果說明了儘管每7個軟體使用者當中就有6個使用非法的產品，但約有75%以上之購買者是受此侵權者影響而採用該軟體，此力量深深地影響到合法軟體的擴散。雖然軟體盜版會使廠商的利潤減少，使得軟體廠商不得不採取軟體保護策略，但由於軟體市場有網路效果存在，有時開放軟體反而是較佳的策略。

　　　　　Software piracy by users has been identified as the worst problem facing the software industry today. And the pervasiveness of software piracy throughout the world is having a profound effect on software publishing industry and the development of digital intellectual properties and technology. Because of this software shadow diffusion, a software firm loses potential profits. However, shadow diffusion the legal diffusion of the software. Software pirates may influence potential software users to adopt the software, and some of these adopters may become buyers. A diffusion modeling approach is suggested to track shadow diffusion and the legal diffusion of a software over time. The approach enables management to estimate the pirated adoptions over time and the percentage of legal adoptions due to the influence of pirates. The modeling approach is applied to study the diffusion of types of software in United Kingdom. The results suggest the diffusion that although six of every seven software users utilized pirated copies, these pirates were responsible for generation more than 75% of new software buyers significantly influencing the legal diffusion of the software. Although software piracy would decrease the profit of software firms, the protection of software is not always a good idea. Owning to network effect, sometimes the software firms should choose not to protect their software.