For all the talk - and the talk has been very loud - of Russian hacking, we've had little evidence presented by the US government.
US intelligence agencies lined up to accuse Russians of hacking into the Democratic National Committee, but withheld detailed evidence.
Fair enough, given it could give away intelligence techniques and sources.
But the indictment of two Russian spies - named as Dmitry Dokuchaev and Igor Sushchin - by the US Justice Department makes the situation different.
To be clear, there is no suggestion that the Yahoo hack is connected to hacking in the presidential election.
But the Department of Justice has laid out clear details of how the Russian FSB - the successor to the KGB - went about one of the biggest hacks in history.
And one of those accused of the hack, Karim Baratov, has been arrested in Canada. That means he's likely to be brought to the US to stand trial.
At that point, the US will lay out its case in forensic detail for the court. That will include exactly how the Russian state goes about hacking.
And how long it's been doing it: the Yahoo hack happened back in 2014.
This case will shine a light on what to date has been a very murky affair.