Wallet.dat (<0.4.0) format: retrieving Bitcoin, possible security concerns Whilst moving houses I came across some old HDDs which I've just found contains a wallet.dat from August 2011. The version of Bitcoin-qt must be 0.4.0 as I know the wallet.dat is password encrypted, which was introduced for version 0.4.0. It is 100% *not* >0.4.0, so the vulnerability patched by 0.4.1 is not in place. 

What is the best way to go about restoring the encrypted addresses? If I were to install the 0.4.1 Bitcoin-qt update, would there be any problems with current OS dependencies? Should I use Windows, Linux? Any input greatly appreciated. (I will certainly keep a backup)
Using wallet /import

If you load the wallet file in a modern Bitcoin Core version, you can use the dumpwallet command (to create an unencrypted dump of the keys), and the importwallet command in a fresh instance with a new empty wallet.dat of the dump. You will need to rescan afterwards, though, which may take a while.

Make sure to wipe the dump file afterwards.

Using db dump/load

One way is to use the following command on a Linux install with db4.8-util installed: db4.8_dump wallet.dat | db4.8_load wallet.dat.new

This will create a new wallet.dat.new file, with the same records as the wallet.dat file, but without any old potentially never-overwritten data.

db4.8-util may be hard to install these days, as most distros stopped distributing db4.8, in favor of 5.1 and later. Bitcoin Core however still uses 4.8 for compatibility reasons. You can use db5.1-util as well, but that means that you'll need a Bitcoin Core version compiled with db5.1 support afterwards to use the newly constructed wallet file.