Thanks Jabo, I think NEM devs are the best devs in crypto town, however the wallet is still too complex. Can you tell me how I can make a back up of my wallet? I mean the NEM wallet operates online or are my coins secure on cold storage on my harddrive? I know these are noob questions, but it's still not quite clear to me...
Crypto 101. There are no coins in crypto. They are only numbers to show quantity and they are all shown on the blockchain, aka ledger or database. The ledger is an immutable and irreversible transaction ledger.
You need keys to unlock and make "changes" to your balance. By "changes" we mean transacting. Technically, it is reducing the number balance you have and incrementing the number balance of the recipient.
So, keys are the main thing to unlock your balance and make transactions. Some keys are stored in the cloud or somewhere, e.g. coinbase, bitpay, etc. for Bitcoin. For NEM, they are stored in your wallet. So, you need to back up your wallet. If you are well versed with the crypto concept, actually you only need to back up the private keys of your wallet accounts. You can reconstruct your wallet with these private keys.
Cold wallet=don't expose your wallet to a network/internet. Hot wallet=exposed. Unique to NEM, warm wallet = exposed to internet, but need another key to sign off, which can be connected off or online.
Hope that helps.
So there are two things that can make it so your coins are lost.
One is if somebody has your wallet and the password to that wallet. Just the password alone, or just the wallet file alone will not ever allow them to access your account and make transfers from your account.
Somebody that has your password, but not your wallet, won't ever be able to recreate your wallet, but somebody that has your wallet file can brute force your wallet file if your password is very weak, just like any other thing that is password protected.
The second thing that could allow somebody to access your account would be if they had access to your private key. The private keys are some of the very important information that the wallet has inside of it, so whether a hacker gets your private key from the wallet file, or just gets the private key by itself, they can access your account.
To me, the private keys are the most important thing to back up. There are loooooong debates of how these should be backed up, whether printed on paper, or stored in a wallet file, or stored in another file format and hidden there. I think it is very important though to have those keys backed up one way or another. I personally print up them on paper (no hacker can get at them that way) and also have a back up of the wallet file with a very long and safe password.
If you would like to make a copy of your wallet file, instructions can be found at
http://blog.nem.io/how-to-find-export-or-delete-your-wallet-and-address-book-file/