Is that Safari on the Mac, or on Windows?
’cos on the Mac, passwords are stored on the Keychain, and if you don't unlock your Keychain in the first place, Safari can't decrypt squat.
The default configuration is for your Keychain to be unlocked when you log in, but you can change that easily enough, and set it to to auto-lock under various circumstances, which means you'll be prompted for your Keychain password whenever Safari wants to auto-fill a login form. Hit Cancel and it won't auto-fill a thing.
If memory serves, other auto-fill data is stored in the same way.


