I moved all my coins to Blockchain, with double passwords (one to get in, another to withdraw)... passwords I have never used before or written down anywhere... very good passwords. Sadly, I can not use Yubikey or 2-pass auth here in Argentina. Nevertheless, I get a message from blockchain at midnight two nights ago saying "Withdrawal from your account".. Of course, I look and yes, the account has been completely wiped out by some address that appears in the ocean off the west African coast.
It sounds like theres a keylogger on your device thats capturing all your passwords. What kind of device did you use to access the acccounts?
Other people have reported passwords being lifted from Android devices. I would not use an Android device to access high value bitcoin accounts. Any amount more than 20BTC should be kept offline.
BTW the address "off the west african coast" is latitude 0, longitude 0, which is the default location for blockchain when the originating IP is unknown.