Browser extensions and phone apps are hot wallets. They sign quickly, connect to apps easily, and are the right tool for active on-chain trading.
The exposure is continuous. Any malware with access to the device, any malicious extension, and any signature you approve without reading can move funds. Attacks rarely need your seed-phrase; a single approval on a fake site is enough.
Practical rule: treat a hot wallet like cash in a pocket. Keep a working balance there, review token-approvals regularly, and route large or long-term positions through a hardware-wallet or cold-storage instead.
Related: cold-storage, hardware-wallet, burner-wallet, wallet-drainer