We recommend that you read the try MultiBit article if you haven't already.
One of the problems with random private keys is that they cannot be easily regenerated. It is for this reason that we, the MultiBit developers, have decided against direct import of a MultiBit Classic wallet. To illustrate this, consider the following example.
Alice imports a collection of random private keys in addition to her wallet words into a combined wallet. Time passes and one day Alice has her computer stolen along with her backups. Fortunately she has her wallet words and so all the bitcoins associated with it can be recovered. However, those bitcoins that remained with the random private keys are only protected by backups which have been stolen as well so they cannot be recovered.
In the remainder of the article we discuss how to safely upgrade from MultiBit Classic to MultiBit and still retain control over old private keys.
If you have a large amount stored in bitcoin (typically over 500 USD worth) then you should seriously consider purchasing a KeepKey device. This will provide the best possible protection for your bitcoins while still enabling you to use them without undue hassle.
You may decide that you want to take this opportunity to split your bitcoin up into smaller amounts and spread them across multiple wallets, each with its own set of wallet words. If you choose to do this then we'd suggest the following approach:
At this point you have a MultiBit receiving address and MultiBit Classic is ready to spend. To ensure that your funds are transferred safely do the following:
Even though all funds have been spent to MultiBit receiving addresses there is still the chance that someone could send you bitcoins using the old address. To ensure that you can always access these funds it is best to maintain a copy of the private keys somewhere safe. There are several approaches to this:
.keyfile to several safe locations (cloud backup, USB stick, etc)
Overall, you should keep a backup copy of the most recent MultiBit Classic installer somewhere safe in case you need it in the future.
Data has a tendency to become lost or corrupted over time so having multiple alternative methods to access the private keys ensures that you have the best possible chance of recovering funds sent to an older address.
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