Once the private key is in your hands you're responsible for the funds. Truly speaking someone might have known about your private keys and passwords. Myself too have experienced loss of funds from my blockchain wallet which happened due to my negligence of keeping private keys securely.
If you carefully read my post, I always double-check and secure it, no one has access to my private keys or passwords. This is the case of the blockchain wallet security, please take some time to read similar posts, it happens these days on a regular basis.
This really is a frustrating experience I must say. I feel your loss. But I also think what
bxmail said isn't wrong. I have used blockchain for close to three years now but I haven't experienced such. This is where I encourage people to always access their wallet through the app and not through web. In all,, we should at all time safeguard our PKey and passwords. You never can tell who is lurking and waiting for the unguarded hour to strike.