@NateEldredge: Plagiarism would not be happened without copyright violation. I hope my last explanations would be comprehensive if my last paragraph on the first answer was not! :)

... See the full description about the C-C licenses here: [creativecommons.org/licenses/]. The file might be in fair-use, which means you can use the work under circumstances. Therefore, see what the license of the work is at first.

@Bakus123: As I wrote before, you must see the license of the file first. There are several kinds of licenses in Wikipedia. For instance, if you are using a file which is in public domain, it means there would be no need to cite it from the copyright aspect, however it is better to do so to increase the reliability of your thesis. But if the file has used a Creative Commons license, then you should notice which kind of license it is. One may allow you to use the content without say a word about the reference, one may does not, or even one just lets you to use for non-commercials...