Earlier quoted context omitted.
An intelligence agency won't declassify how they determined who it was. That would compromise their ability to use the same method (informant, vulnerability, etc) in the future. They are standard techniques. It doesn't say they are unique. Just that this hacker relies on these specific standard techniques as opposed to other ones.
>An intelligence agency won't declassify how they determined who it was. Yeah, just like a weapon of mass destruction in Iraq. We can't tell how we got this information, but we know for sure. Then few years later it turns out there is no WMD found. Ooops. Sorry. Give me a reason to trust them again?
First, the people making the DNC hack report are not the same as the analysts who worked on Iraq. The IC is not a monolith.
Second, the Bush White House saw the intelligence they wanted to see.
Third, burning sources and methods is a very real concern in intelligence gathering. That reality can't be ignored no matter how much you want information to be free and open.
You don't have to trust the IC. In fact you probably shouldn't take what they say at face value. But there are very good reasons for why they operate the way they do.