The IB document on IB is updated regularly. For the most authoritative version, please check the OCC (Academic Honesty page).

IBO Documents

DP regulations - see Section 30 page 10
see also section 5.2, 5.3, 5.6 re the use of student's work by IBO after submission, even though the students retain copyright, IBO has the right to use the submitted work ...... read it and let the students know their rights ....
MYP Regulations - Section C, article 20, page7

No PYP mention of malpractise ....?

New supporting IB document on Academic Honesty (2012).

What is plagiarism and how to prevent it ?

All about plagiarism

At the following website you can find answers to a number a question about plagiarism:
What is plagiarism?
What are major types of plagiarism?
Why do students plagiarize?
How to prevent plagiarism?

NSW Plagiarism education Program
All my own work - HSC program compulsory for students, usually run by librarians

Different types of plagiarism (presentation)

Search, Plagiarism, Cites

Avoiding plagiarism (animation)

You Quote It, You Note It! Explains the basics of avoiding plagiarism by learning why, when, and how to cite.

Combating plagiarism (presentation)

What is Turnitin?

Turnitin is online web-based text-matching software that works by comparing electronically submitted papers to billions of pages of content located on the Internet and proprietary databases as well as the work of other students whose papers have also been submitted into the system.

Turnitin Guide

Video Tutorial On Using Turnitin

Other ways to detect plagiarism

Using a Search Engine to Detect Plagiarism

Using Google as a Detection Service

Bibliography tools

The OWL (Online Writing Lab) at Purdue University: Research and Citation

Online Citation Tools
Landmark's Citation Machine - for high school, college, and university students
KnightCite Bibliography Composer (MLA, APA or Chicago citation style) KnightCite is an online citation generator
OSLIS MLA Online Elementary Citation Maker

NSW Department of Edcation of School Education, Handbook for School Libraries, Updated and republished online 2008