Similar to what occurs in literature, art and other human endeavours, every scientific report is based in previous work done by others. The new paper should add something original but a basic law of scientific honesty demands that any mention ideas, observations or thinking that has been previously proposed or published by others, should be acknowledged properly in the text and in the references. Plagiarism is identified when the authors of a scientific report use ideas or text that belong to others and present them as original, the previous source is concealed or it is referred to in a different context. The authors of a paper that contains plagiarism have the intention to mislead the readers, pretending to be the original authors of an idea that was expressed previously by others, or to be the owners of results shown by them. Plagiarism is a dishonest behaviour and, when discovered, may have dangerous consequences because the editors of the journal may publish a notice of retraction that will be inserted by Medline in both papers: the plagiarized and the plagiarizer, to be noticed by everyone who accesses to either of them in the Internet.