A variety of free and commercial software applications designed to detect plagiarism from Internet sources has appeared in recent years. However, their effectiveness and impact on student behaviour has been assumed rather than confirmed. The study presented here explores the responses and perceptions of a group of first year students at an Irish university after their first contact with anti-plagiarism software in the context of peer-reviewed assignments. The results indicate that the use of anti-plagiarism software led to a decrease in Internet plagiarism and to lower grades being awarded in peer reviews. Additionally, students were found to have a positive attitude towards the anti-plagiarism software in the context of peer reviewed assignments. Implications for educators on the use of this software are discussed. (Contains 3 tables and 1 figure.)