Security vendor Mandiant's 60-page report on Chinese cyberespionage, which offers proof that it is coming from a Chinese military unit housed in a building in the Pudong district of Shanghai, adds new fuel to two hotly debated cybersecurity questions.

First, does this mean the quest for 100% certainty in "attribution" of intrusions has been achieved? And second, does that mean the U.S. is justified in taking what government officials like to call "active defense" measures -- what most others call "retaliation" or "offense"?

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