It is 'confirmed' from the first block like you say, but its not considered secure or confirmed in some other platforms.
There really should be n amount of confirmations before its considered confirmed|secure, but thats for you and your system to decide. for example - I think bitcoin uses 6 confirmations - 6 blocks deep until its confirmed? When it comes to miners and the rewards, I believe its 10 blocks until it can be spent?
On multichain this is dependent on some mining settings or if its on a single node that can mine. If mining is done as a round robin or a single node is mining, the transactions is confirmed immediately. It is still insecure, until the next block writes on top. The next block (if mine empty rounds is on), will confirm in one hour 6 times, which usually enough security. If you dont mine additional blocks and the last block is confirmed only once, its vulnerable - unless of course you are the only miner with permissions where then it wont really matter.