The 2016 hacking

[JHB]

9. Yes, DU was hacked on election night, leaving only a RW video...

...which practically shouted that it was from a European group (the choices of images were way off from the sort of things US-based wingnuts would select).

It took a while (a few weeks, IIRC) to identify what they exploited and institute fixes that wouldn't let them do the same thing again.

I don't think any individuals or groups have claimed responsibility, but aside from general malice it's assumed it was partly to disrupt information-sharing and organizing about the electoral malfeasance at work.