I have a blockchain.info wallet. Last night I decided to set up a wallet for my daughter so I signed out of my account. Created one for her and then had difficulty signing in to mine, I had about 8 attempts then gave up. I then noticed in my email I had an email from blockchain telling me of each of the failed attempts which was me. I then managed to get into my wallet and 99% of my BTC had gone. Is this a security feature or has someone stolen them? Thanks. I have checked the new wallet in case they were there but sadly they are not.
Blockchain.info's My Wallet stores your Bitcoin wallet in encrypted form. This means that anyone that knows your wallet identifier can retrieve the encrypted form of your wallet. One can of course only use/open the wallet with the encryption password.
This does however mean that anyone that retrieved your wallet identifier can try to guess your password as many times as they want. Once they got the encrypted version of your wallet, they can use smart brute force techniques to crack your password.
So, you could have been hacked if both
- Someone got hands on your wallet identifier. Maybe you mailed it or mentioned it somewhere. Maybe you got malware or a spoofing browser extension.
- You have a weak password so that regular password crackers were able to find your password fairly easily. Try to avoid passwords consisting of only existing words or only lower case characters f.e.