Circle's freeze of about $823 million in USDC is the second-largest issuer intervention in the Binance hack, and its meaning lies as much in what it could not touch as in what it did.

USDC can be frozen because Circle issues it and can block flagged addresses, a tool that proved effective for a very large sum.

The theft, however, had already branched into territory where that tool does not apply, with about $786 million in stablecoins converted into ETH and TRX before the freezes.

Elliptic, a blockchain analytics firm, puts the total frozen figure at about $2.84 billion, while Binance puts it at about $3 billion, both short of the overall hack estimate of about $6.3 billion.

A further movement, reported by LlamaRisk, saw about $59.9 million in stolen USDT used as collateral on Aave, supporting borrowing of about $43.8 million worth of ETH.

Most consequentially, Elliptic estimates about $3.33 billion in assets remains controlled by the attacker and cannot be frozen by a centralised token issuer.

For the investigation, then, the Circle freeze is a major recovery step that still leaves the central challenge intact: USDT and USDC can be frozen by their issuers, ETH and Bitcoin have no central issuer with that same power, and the unfrozen billions are the bigger story.