There are free plagiarism programs, such as Viper, Anti-Plagiarist, but in reviews in CNET, EDUCAUSE, most are not well-supported. And one can use Google to catch plagiarism, but it will not address surrounding issues, such as what constitutes plagiarism, what guidelines help students to prevent plagiarizing, how does plagiarism harm the academic community.
Claremont McKenna College conducted a survey of faculty and students to determine preferences for several plagiarism prevention programs. None of the evaluated programs addressed ethical issues of plagiarism or taught students what plagiarism looks like very well and it was recommended that free resources available online such as the “Understanding Plagiarism" module from Prentice Hall, Purdue OWL and iParadigms fared about as well as fee-based programs.
Claremont Mackenna’s survey results led the committee to strongly recommend Turnitin for plagiarism detection.
I’d recommend to the faculty that the university purchase subscriptions to Turnitin for all of our students and faculty and that faculty pursue free resources online to address plagiarism issues in class. Feel free to contact me on either of these issues.
The following questions may be used to guide in choosing plagiarism detection and prevention software.
Is the interface intuitive?
Is the time commitment posed by this program reasonable? (Will you and your students use it?)
Does the software provide useful information about plagiarism and academic honesty generally?
Does the software help students to understand the harm done to the college community by plagiarism?
Resources for Students
One of the best for plagiarism prevention and all-around writing
Basic Rules for Avoiding Plagiarism, Prentice Hall
The Golden Rule for Avoiding Plagiarism—Give Credit Where Credit is Due
Basically, there is only one way to avoid plagiarism—give credit to a source whenever you use information that is not your own unless it is common knowledge.