How contract migration works

Summary: Trail of Bits describes a two-step smart contract migration procedure: read data from a block before the incident, then write it to a newly deployed contract, with the Bancor and KICKICO hacks cited as cases where stolen private keys left deployed contracts unfixable. The post puts the cost of migrating one ERC20 balance at roughly $0.025, with a 200-account batch transfer costing around 2.4M gas, or $5.04 at 10 Gwei.
Bottom line: The post's own figures put migration of a single token balance at about $0.025, so the real exposure is not the gas bill but the operational step of coordinating with exchanges to list the new contract and discard the old one. A stolen owner key, as in the Bancor and KICKICO hacks, can leave a contract unfixable even when an upgradability mechanism exists.

Read the original at Trail of Bits Blog ↗