heres a few more of the 3 letter accounts
Sync: sony amount 20.3924504 MCZ on 2015-02-12 17:24:46
Sync: net amount 21 MCZ on 2015-02-12 17:37:19
Sync: day amount 21 MCZ on 2015-02-12 17:28:50
Sync: sun amount 20.3158655 MCZ on 2015-02-12 17:22:00

its seems like a script or bot perhaps in android emulator?  set to continuously farm and automatically create new accounts.

What if after install or a reinstall of app the user needs to be issued a "key" which is generated by server using some crypto magic that involves the phone number/imei/deviceid and sent to them via sms before they are allowed to mine or sync.  The key cant be faked and once used is linked to their account permanent to prevent any attempt to reuse the key more then one account.  Wouldn't something like that prevent these types of exploits?