They don't provide the server-side code, nor a way to ensure that your client is talking to a specific server. The only authentication is via a 5 digit code sen

They don't provide the server-side code, nor a way to ensure that your client is talking to a specific server. The only authentication is via a 5 digit code sent via SMS, so it's presumably very easy to spoof and control messages. You need on average 5000 attempts to log into another users account (they are send a "new device added" notification message though), which could be done reasonably easily if you knew a person would have their phone off for a period of time when you wanted to attack their account.