This is simply a security measure when creating a Service NSW online account - with your security code number - for accessing your Services NSW account.

got a message with a code . f*ck knows why

Nah, not an overseas hack. This is a security measure when creating a Service NSW online account and you forget your password, they send you a security code to confirm it's you. If you got this text message and you haven't been doing this or resetting your password for a Service NSW Account, then it's probably someone that has put your number in by error.

Just received this "Service NSW agency linking. Your security code is: (there was a six digit number here) Please don't reply by message.

I rang the number and the message says "the number you have called is disconnected".

Any ideas? Thinking it might be an overseas hack.