b14g, a Bitcoin staking protocol on Core, says about 97 million CORE staked through it just walked out the door to attacker-controlled addresses.
The team paused the affected contracts once it noticed. Its own tracking puts about 68 million of the CORE still sitting on the Core chain, and exchange partners have frozen roughly 9 million tied to the attacker. Frozen isn't recovered, and no technical cause has been published yet; an incident report is promised.
The BTC side was untouched, b14g says, because it never left Bitcoin. It stays time-locked there while CORE does the moving around.
The Bitcoin was safe for the one reason it couldn't go anywhere. Apparently that's the feature.
Source: TechFlow