Bitcoin Q&A: Multi-signature and Distributed Storage

What happens when wallets (personal or at an exchange) are hacked? What is "sweeping" with regards to private keys? After a hack, is it possible to track the stolen bitcoin and identify the hacker? How do you keep bitcoin safe in a group / corporate environment? Is it possible to create a multi-signature setup with Trezor and Electrum? Could passphrases be brute-forced? What is happening with browser extension deprecation?