I heard some rumors about bots being hijacked to post Nazi spam. Any validity to this? If so, what can be done to protect against it?

I'm hearing this third-hand, so no specific events or screen-shots to refer to, just a lot of "my friend in another server heard from their friend in another server...".

So I figured I'd ask here to see if anyone knows what this is about, and if there's anything we can do about it.