A Chinese headmaster has been fired after a secret stack of crypto-currency mining machines was found connected to his school's electricity supply.
Teachers at the school in Hunan became suspicious of a whirring noise that continued day and night, local media report.
This led to the discovery of the machines, which were mining the crypto-currency Ethereum.
They racked up an electricity bill of 14,700 yuan (£1,600).
The excessive electricity consumption had previously been reported to the headmaster, Lei Hua, but he reportedly dismissed it as being caused by air conditioners and heating devices.
Mining crypto-currencies such as Bitcoin and Ethereum involves connecting computers, usually specialised "mining machines", to the currency network.
By providing computing power for validating transactions on that network, mining-machine owners are rewarded with newly generated coins, making it a potentially lucrative exercise - especially when done at scale.
