First, never leave your bitcoins sitting in someone else's privkey. Second, know your own privkeys.

Never leave your bitcoins sitting in someone else's privkey. It is hearbreaking to read daily stories from people whose bitcoins were stolen from moneychanger accounts. Here is the problem. Many of you routinely trust your bank, stockbroker, or Paypal with your money. You are so used to doing this without thinking, that you leave bitcoins sitting in your account with Mtgox, CampBX, Bitfloor, or other moneychanger. This makes it likely that a thief will figure out your user-ID and password, or penetrate the moneychanger's security, and will siphon off your bitcoins. It is pointless to blame the moneychanger. Bitcoins are too new for moneychangers to have the same FDIC protection as banks, credit unions, or brokerages. It is pointless to blame the bitcoin protocol, the miners, or the developers. The bitcoin concept makes you alone responsible for your money.

The bitcoin concept pivots on the breakthrough idea that everyone is capable of receiving, storing, and sending money on his or her own without interference by anyone else. If you embrace the concept and accept the responsibility, you will transfer bitcoins away from the moneychanger to your own address within seconds after buying them. If you do this, and keep your privkey secret from anyone else, it will be impossible for anyone to steal your bitcoins. Bitcoins that you leave in a moneychanger account are sitting in the moneychanger's privkey. Again, never leave your bitcoins sitting in someone else's privkey.

Second, know your own privkeys. By now you should understand that bitcoins are not stored in your wallet. They are not in your computer, nor on its hard drive, nor on a flashdrive. Your bitcoins are in "the cloud". You can spend them only by knowing their privkey and loading that privkey into "sending" software. The "sending" software transfers the coins from your privkey in the cloud to someone else's address in the cloud. Which brand of sending software you use is unimportant. Whether the sending sofware contains the blockchain or uses a server is unimportant. Whether the sending software resides on your computer, tablet, smartphone, or on someone's website is unimportant. The only thing that is important is that you should know your own privkeys. If you know your privkeys, you can spend your bitcoins even if your house burns to the ground. If you do not know your own privkeys, your money is lost forever. A wallet is nothing more than a handy place to hold a copy of your privkeys. There is nothing wrong with storing your privkeys in a wallet (as well as in eight or nine other secret places). But to store your privkeys in a wallet instead of knowing them is the height of foolishness. If you know your privkeys and lose your wallet, you can simply import them into a new wallet. But if you lose your wallet and do not know the privkeys that it held, your money is lost forever. Again, know your own privkeys.