When in doubt, ask. Covering Your Tracks With any citation you add to your paper, you are communicating several things. In addition to tipping your hat symbolically to this authority on the subject about which you're writing, the citation also provides the reader with precise directions to how to find the source of your information, either so the reader can call your bluff and see if this information really exists in this form or so the reader can track down the source for further enlightenment. What this means is that you must be very careful to give accurate, detailed information on how to locate the source you've cited. With books and journal articles, this information is so standard and so easily accessed that we have begun to take for granted the relatively small amount of information that makes finding these sources possible.
Electronic sources are typically more complicated and require greater care.
When you have decided that it is appropriate to use information from an Internet source, be as specific as you can about pinpointing how someone else can track down that same information. Say, for instance, that you are writing a paper on Abstract Expressionism. Notice that only the writer's last name is cited here. 4 Mar. 1997. You can look it up, as they say.