Local geth computations are too fast. 70 Eth from several hours

Hello everybody. I am absolute noob in mining so i have several questions. I download etherminer and geth.
I create a new account personal.newAccount("password")
Then i unlock it personal.unlockAccount(address, "password")
Then i start geth: geth --rpc --rpcaddr "My IP" --rpcport 8545 console
I connect several PC to this IP and start mining.
After several hours check web3.fromWei(eth.getBalance(eth.coinbase), "ether")
i have 50.

So my problem is: it seems i compute inside my local network and my ETH costs nothing.
I could not perfom any transfer (

How to compute solo properly?
How should i check whether my ETH are real?

P.S. I don't want to connect to pool because it is work computers and i want avoid attention of our sysadmin.

Thank you in advance!!!