[r3bl]

What would you consider as a confirmation? Without someone coming out and saying "we're the ones who did it", it's very unlikely that it'll be ever be confirmed.

The best you can do is to make some educated guesses (by looking at the timestamps, coding patterns, comments in the code, who might be interested in hacking the target, political connotation to the attacks etc.). That's usually how state-sponsored attacks get attributed.

For example, "Guccifer" used GTM+3 settings and attacked DNC a few hours after Trump publicly "hoped" that Russians will find the emails. That doesn't confirm that it was sponsored by Russia, but it makes it an educated guess.