Because the second sentence says the students WERE passed the exam last week and <em>were</em> doesn't need to be in there. Therefore it is not correct.
But while it is true the Internet has made it easier for students to plagiarize, it's easy to forget that the Web is not as new of a technology as many seem to think. On the other hand, it's made plagiarism much easier to detect and prevent, creating tools to both catch mistakes and stop those who are acting in bad faith.
