How, precisely, does this information do "serious damage...", as you say. We already knew that the NSA can hack computers and cell phones; the article is simply more of the same.
So "serious" damage is probably too far. But how does this benefit the American people? The US has pretty good reasons for keeping such an effort covert, and this stuff doesn't come across as an affront to people's privacy and freedoms, not like the domestic surveillance programs did.