MLA Works Cited: Electronic Sources (Web Publications)
MLA lists electronic sources as Web Publications. Thus, when including the medium of publication for electronic sources, list the medium as Web.
It is always a good idea to maintain personal copies of electronic information, when possible. It is good practice to print or save Web pages or, better, using a program like Adobe Acrobat, to keep your own copies for future reference. Most Web browsers will include URL/electronic address information when you print, which makes later reference easy. Also, you might use the Bookmark function in your Web browser in order to return to documents more easily.