Bitcoin - Core Wallet.dat

If your PC has a keylogger or screen grabber, your encryption passphrase will be stolen the moment you type it. Never decrypt your wallet on a compromised machine.

Contrary to what beginners might think, your Bitcoin isn't actually "in" your wallet software. The Bitcoin exists on the blockchain ledger. The wallet.dat file holds the keys (specifically, the elliptic curve private keys) that prove you own the addresses on that ledger. Bitcoin Core Wallet.dat