thanks a lot, it is now understood.
and yes, my testnet wallet.dat is exactly 96 bytes.
another question:
is it enough to backup wallet.dat + dnet_ket.dat in order to make a backup for my account ? or are there more files i need to backup ?
In case of data loss, it is enough to back up only the file wallet.dat. The file dnet_key.dat identifies your host on the network, but has nothing to do with coins. But since private keys generates from the random data saved in the dnet_key.dat file, someone, having captured the file dnet_key.dat, can restore your keys.
Therefore, both files wallet.dat and dnet_key.dat should be kept secret. Probably, it makes sense also to save the file netdb.txt. It contains the ip addresses and ports of servers running on the network. Other files do not need to be backed up or in secret storage.
1. I have transferred 100000 coins to the address YjZxlonGl+tSjibh1GJr5//Cydlo9Uvn. But you probably can see them after synchronizing with the network.
I think that is not secure. maybe add password or smth to encrypt personal wallet and/or dnet_key and can start only when manually password is entered with some option to be not secure and be more secure? like repeat password within some user specified time period after last time pass was entered - time frame should be defined by network sync (or smth like you probably know better).