Specific guidelines on citing electronic references are provided on pages 268-281 of the APA's Publication Manual 5th edition:
American Psychological Association. (2001). Publication manual. (5th ed.). Washington, DC: American Psychological Association. 
Short Loan Collection 2-hour and 3-day loan 808.06615 A51 2001
General Library Science (and Arts) Reference 808.06615 A51 2001
Tamaki Reference 808.02 P97 2001

The APA updated these guidelines in 2007 in the APA Style Guide to Electronic References. [Note that users may print copies for personal use only].

Further updated information on how to cite electronic references and provide citations in the text of electronic material is provided by the American Psychological Association on their web site: 

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