My Lawyer Says I Can Hurt You

The U.S. Air Force recently announced that its lawyers were hard at work to make sure that all its Cyber War activities were legal, including the classified ones (which are most of them). However, the air force pointed out that just seeking information stored on foreign computers does not require this kind of legal review, only those Cyber War operations that seek, "…to disrupt, deny, degrade, negate, impair or destroy adversarial computer systems, data, activities or capabilities." 

This air force announcement, in the form of a policy directive, is a pre-emptive strike. That's because there is not yet any solid law covering many Cyber War operations. At the same time, American Cyber War commanders refuse to comment on the existence of U.S. offensive Cyber War weapons. When pressed on this by members of Congress, the Cyber War officials said that the answer could only come in a closed (classified) meeting.

http://www.strategypage.com/htmw/htmurph/articles/20110817.aspx