I've got my bitcoin in cool storage - basically in an encrypted virtual machine on a separate computer (bare metal hypervisor) from my main machine. I've done a video on this in the Electrum forum if you're interested in the details. Anyway, I think it's pretty secure. I have a watching only electrum wallet on my main PC which I look at from time to time, and I also have my addresses including the next five deterministic addresses in my blockchain.info wallet.

I sent a donation to Andreas's Dorian fund from cool storage using my USB stick to get to my private keys and all was well, everything went through as expected. I logged in to my blockchain.info wallet last night and noticed that there were some significant BTC missing from my wallet.  

I started to panic thinking that my cool storage had been compromised, but I couldn't understand how because the cool storage VM is always powered off unless I want to spend. Also, only one address had been drained, all my other addresses were fine.

Can you guess what the problem was? The BTC were not stolen.

Come on, what was it? Guess before continuing...

















I had forgotten about how change addresses work. Sure enough my wallet was complete when I expanded the change addresses section in electrum. I have now added my change addresses as watching addresses in blockchain.info and my balance is exactly how I expected, nothing missing.

Just thought I'd tell my story, because my heart was really racing last night! Anyone had a similar experience?