Much of the data stored on computers, such as the data stored in random access memory (RAM) and internet caches, is temporary and "ephemeral". Because these temporary, transient files are deleted as often as every few hours, it would seem that there would not be a duty to preserve them.
However, in Columbia Pictures Indus. Inc. v. Bunnell
, 2007 U.S. Dist. LEXIS 46364 (C.D. Cal. June 19, 2007) Magistrate Judge Jacqueline Choolijan, following Ninth Circuit precedent, ordered the defendants to preserve data "stored" in RAM. The court held that the server log data (IP addresses, etc.) stored in RAM was extremely relevant stored information under Rule 34 of the Federal Rules of Civil Procedure.
Many commentators have been alarmed by the Bunnell decision, fearing that the preservation of electronically stored data would become "paralyzing" if it required the preservation of all temporary and ephemeral files. However, some commentators have indicated that a closer read of the opinion illustrates that the preservation of ephemeral data may be limited to a narrow set of circumstances. For further commentary, check out this article by Conrad J. Jacoby on LLRX.com (Law and Technology Resources for Legal Professionals.)
The lesson? Examine your electronic discovery obligations early -- as soon as you have notice of a duty to preserve -- and get an agreement from opposing counsel regarding the scope of your duty and what types of electronic information you have to keep.