There's been a half-a-billion dollar hack of a bridge between Eth and one of it's side-chains "Ronin"
https://roninblockchain.substack.com/p/community-alert-ronin-validators
Not really sure of most of this but:
Axie Infinity is some kind of blockchain card-trading game. You can take your blockchain tokens and fight them against other blockchain tokens or mutate and breed them or something. And there's a website with graphics to try and make that an interesting thing to happen.
Eth transactions are crazy expensive coz of it's limited blockchain space. Far too expensive to merge Axie tokens etc. So I guess they want their trading game to operate on a side-chain . That's called "Ronin". The Ronin network is less congested coz it's only really got the Axie game on it, and presumably it compromises decentralization for throughput.
You can transport your Eth into that "Ronin" network, play around with the game using cheep network fees, and then teleport what remains back out after you've won/lost.
But this is the trouble with the multi-chain systems: There isn't really a way to teleport Eth off it's chain and into another one. All you can do is have a "bridge", some computers that lock up Eth on the Eth chain while issuing another Ronin-Eth token on the other chain.
Counter-party risk.
Which means you end up with this gigantic honey-pot where all the _REAL_ Eth is, and if you can hack that then you can move the Eth around it's real network while leaving the Ronin network bridge with debts it can't pay.
They say someone "hacked" the private keys of a computer on the network bridge. Not clear what that means. Presumably the hackers somehow gained access to a computer where the keys were stored, if it wasn't an inside job.
So now the Ronin Network Bridge has half a billion dollars fewer assets on Eth than it has liabilities on Ronin Network.
In the fiat world they do that on purpose and call it "fractional reserve" of course.